devstack: move all logs to /var/log/gnocchi
devstack: move all logs to /var/log/gnocchi

Change-Id: Iba4261d552ff8f2327ede617428bad1ccae55919

sileht/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi,gnocchixyz/gnocchi,leandroreox/gnocchi,leandroreox/gnocchi