ceph-volume: reduce log verbosity

inventory/list logs every lsblk/pvs/bluestore probe at info, that's
why the ceph-volume log file gets huge.
Those traces are debug. info stays for actual OSD work (create/zap/activate).
if a command fails we still dump it at warning so you don't need --log-level
debug to see what broke.

default --log-level is info now.

Fixes: https://tracker.ceph.com/issues/73725

Signed-off-by: Guillaume Abrioux <gabrioux@ibm.com>