[Nexthop] Run_test option to run on reference board

**Pre-submission checklist**
- [x] I've ran the linters locally and fixed lint errors related to the
files I modified in this PR. You can install the linters by running `pip
install -r requirements-dev.txt && pre-commit install`
- [x] `pre-commit run`

Explicitly control when the config should be modified to set
AUTOLOAD_BOARD_SETTINGS instead of autodetecting montblanc since not all
montblancs are reference boards. As well, modified a copy of the
original config to preserve the original and passed in the copy to the
tests.

Verified the help output:
```
[root@fboss101 fboss]# ./bin/run_test.py --help
Setting fboss environment variables
usage: run_test.py [-h] [--coldboot_only] [--filter FILTER] [--filter_file FILTER_FILE] [--list_tests] [--config CONFIG] [--qsfp-config QSFP_CONFIG] [--sai_replayer_logging SAI_REPLAYER_LOGGING]
                   [--skip-known-bad-tests SKIP_KNOWN_BAD_TESTS] [--known-bad-tests-file KNOWN_BAD_TESTS_FILE] [--unsupported-tests-file UNSUPPORTED_TESTS_FILE] [--mgmt-if MGMT_IF] [--sai-bin SAI_BIN] [--oss]
                   [--no-oss] [--fruid-path FRUID_PATH] [--simulator SIMULATOR] [--sai_logging SAI_LOGGING] [--fboss_logging FBOSS_LOGGING] [--setup-for-coldboot SETUP_FOR_COLDBOOT]
                   [--setup-for-warmboot SETUP_FOR_WARMBOOT] [--run-on-reference-board]
                   {bcm,sai,qsfp,link,sai_agent} ...

Run tests.
...
  --setup-for-warmboot SETUP_FOR_WARMBOOT
                        run script before warm boot run
  --run-on-reference-board
                        Modify SAI settings to run on reference board instead of real product
```

Ran the script with the option enabled, verified that a copy of the
config was made and the original remained unchanged.
```
[root@fboss101 fboss]# ./bin/run_test.py sai --filter=*HwEmptyTest.CheckInit* --config /opt/fboss/share/hw_test_configs/montblanc.agent.materialized_JSON --run-on-reference-board
Setting fboss environment variables
The --skip-known-bad-tests option is not set, therefore unsupported tests will be run.
HwEmptyTest.
  CheckInit

Using a modified config file {self._config_file_modified} for test runs
Replaced AUTOLOAD_BOARD_SETTINGS: 0 by AUTOLOAD_BOARD_SETTINGS: 1 in file /tmp/modified-montblanc.agent.materialized_JSON
...
[root@fboss101 fboss]# grep -l 'AUTOLOAD_BOARD_SETTINGS: 1' /tmp/modified-montblanc.agent.materialized_JSON
/tmp/modified-montblanc.agent.materialized_JSON
[root@fboss101 fboss]# grep -l 'AUTOLOAD_BOARD_SETTINGS: 0' /tmp/modified-montblanc.agent.materialized_JSON
[root@fboss101 fboss]# grep -l 'AUTOLOAD_BOARD_SETTINGS: 1' /opt/fboss/share/hw_test_configs/montblanc.agent.materialized_JSON
[root@fboss101 fboss]# grep -l 'AUTOLOAD_BOARD_SETTINGS: 0' /opt/fboss/share/hw_test_configs/montblanc.agent.materialized_JSON
/opt/fboss/share/hw_test_configs/montblanc.agent.materialized_JSON
[root@fboss101 fboss]#
```

Author: anna-nexthop

fboss/oss/scripts/run_scripts/run_test.py

@@ -7,6 +7,7 @@
 import json
 import os
 import re
+import shutil
 import subprocess
 import sys
 import time
@@ -284,6 +285,10 @@ class TestRunner(abc.ABC):
         re.VERBOSE,
     )
 
+    def __init__(self):
+        super().__init__()
+        self._config_file_modified = None
+
     @abc.abstractmethod
     def _get_config_path(self):
         pass
@@ -621,7 +626,31 @@ def _replace_string_in_file(self, file_path, old_str, new_str):
         except Exception as e:
             print(f"Error when replacing string in {file_path}: {str(e)}")
 
-    def _run_tests(self, tests_to_run, args):
+    def _backup_and_modify_config(self, conf_file):
+        """Create a copy of the config and modify settings"""
+        if args.run_on_reference_board:
+            # Create a copy of the config file for modification
+            try:
+                # Create a modified copy in /tmp with standard name
+                config_filename = os.path.basename(conf_file)
+                self._config_file_modified = f"/tmp/modified-{config_filename}"
+                shutil.copy2(conf_file, self._config_file_modified)
+
+                print("Using a modified config file {self._config_file_modified} for test runs")
+                # Some platforms, like TH5 SVK, need to set
+                # AUTOLOAD_BOARD_SETTINGS=1 to autodetect reference board
+                self._replace_string_in_file(
+                    self._config_file_modified,
+                    "AUTOLOAD_BOARD_SETTINGS: 0",
+                    "AUTOLOAD_BOARD_SETTINGS: 1",
+                )
+                return self._config_file_modified
+            except Exception as e:
+                print(f"Error creating config copy {conf_file}: {str(e)}")
+                return conf_file
+        return conf_file
+
+    def _run_tests(self, tests_to_run, conf_file, args):
         if args.sai_replayer_logging:
             if os.path.isdir(args.sai_replayer_logging) or os.path.isfile(
                 args.sai_replayer_logging
@@ -662,14 +691,6 @@ def _run_tests(self, tests_to_run, args):
             warmboot = True
 
         test_binary_name = self._get_test_binary_name()
-        conf_file = (
-            args.config if (args.config is not None) else self._get_config_path()
-        )
-        if args.oss and self._string_in_file(args.fruid_path, "MONTBLANC"):
-            # TH5 SVK platform need to set AUTOLOAD_BOARD_SETTINGS=1
-            self._replace_string_in_file(
-                conf_file, "AUTOLOAD_BOARD_SETTINGS: 0", "AUTOLOAD_BOARD_SETTINGS: 1"
-            )
         if test_binary_name != "qsfp_hw_test" and not os.path.exists(conf_file):
             print("########## Conf file not found: " + conf_file)
             return []
@@ -773,7 +794,11 @@ def run_test(self, args):
         # Check if tests need to be run or only listed
         if args.list_tests is False:
             start_time = datetime.now()
-            output = self._run_tests(tests_to_run, args)
+            original_conf_file = (
+                args.config if (args.config is not None) else self._get_config_path()
+            )
+            conf_file = self._backup_and_modify_config(original_conf_file)
+            output = self._run_tests(tests_to_run, conf_file, args)
             end_time = datetime.now()
             delta_time = end_time - start_time
             print(
@@ -1419,6 +1444,12 @@ def _filter_tests(self, tests: List[str]) -> List[str]:
         default=DEFAULT_TEST_RUN_TIMEOUT_IN_SECOND,
         help="Specify test run timeout in seconds",
     )
+    ap.add_argument(
+        "--run-on-reference-board",
+        action="store_true",
+        help="Modify SAI settings to run on reference board instead of real product",
+        default=False,
+    )
 
     # Add subparsers for different test types
     subparsers = ap.add_subparsers()