integration-test: Sleep for a while after mdraid creation

Integration tests are missing synchronization mechanisms and waiting
for an object to appear on the bus. Thus for now, add a nasty sleep.

  ======================================================================
  FAIL: test_md_raid_methods (__main__.MDRaid.test_md_raid_methods)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "/home/tbzatek/devel/udisks/src/tests/integration-test", line 1855, in test_md_raid_methods
      self.assertIsNotNone(block)
      ~~~~~~~~~~~~~~~~~~~~^^^^^^^
  AssertionError: unexpectedly None

Author: tbzatek

src/tests/integration-test

@@ -1831,6 +1831,7 @@ class MDRaid(UDisksTestCase):
         create.extend(self.md_legs)
         self.assertEqual(subprocess.call(create), 0)
         self.sync()
+        time.sleep(2)  # FIXME: find a better way
 
     def tearDown(self):
         self.assertEqual(