qa/common.check: add _need_metric()
qa/common.check: add _need_metric()

Can be used to ensure any unusual metrics required by a QA test are
available from the local pmcd ... if there is not at least one value
then we _notrun with an appropriate message.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp