Fix test_metric_file_override metric from backend
Fix test_metric_file_override metric from backend

Fix the list of required metrics from a datasource when testing the
existence of this metric in the metric map.

Change-Id: I19b7408a98893bc942c32edb09f1b3798ec8dc79

stackforge/watcher,stackforge/watcher,openstack/watcher,openstack/watcher