Don't translate debug level logs in nova.volume

Our translation policy
(https://wiki.openstack.org/wiki/LoggingStandards#Log_Translation) calls
for not translating debug level logs. This is to help prioritize log
translation. Furthermore translation has a performance overhead, even if
the log isn't used (since nova doesn't support lazy translation yet).

Change-Id: Ib529afea4d1696d8905e2d533803562130950d83
Merge "Don't translate debug level logs in nova.volume"