rest: fix typo in metric policy
rest: fix typo in metric policy

Change-Id: I54a0f48214b5f8c283b121a64907e2f0e212002f

idegtiarov/gnocchi-rep,idegtiarov/gnocchi-rep,sileht/gnocchi,idegtiarov/gnocchi-rep,leandroreox/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi,leandroreox/gnocchi,gnocchixyz/gnocchi