NBS-3049 report when there are no active faults

[cdavis-joy]

Tested on US cluster:

# HELP solidfire_cluster_active_faults List of any active faults detected on the cluster
# TYPE solidfire_cluster_active_faults gauge
solidfire_cluster_active_faults{code="",details="",drive_id="",node_hardware_fault_id="",node_id="",node_name="",resolved="",service_id="",severity="",type=""} 0