If an OpenStackBaremetalSet ends up with "unassigned" BaremetalHost hostRefs in its status, a recently-added validation check will prevent further reconciliation for that OSBMS.  This check was added to guard against the propagation of errors if a user deleted an underlying BaremetalHost without using the proper OSBMS workflow.  Unfortunately, errors encountered during the OSBMS reconcile loop can cause "unassigned" entries to creep into the OSBMS status which then are treated by the validation check as if they were improperly-deleted BaremetalHost hostRef entries.  We need to change the validation check so that it ignores "unassigned" hostRef entries.