need to clear errors when replication is restarted successfully

As part of fix for MB-14501, pipeline errors are cleared when pipeline is restarted.

pipeline_manager.go:
if pipeline_mgr.reportFixed(r) == nil

The clear error op in rep_status.ClearErrors() was unexpectedly removed in a later checkin, the fix for MB-14564, though.

Need to add rep_status.ClearErrors() back to restore the original functionality.