common/common_init: start log from common_init_finish (if not yet started)

common/common_init: start log from common_init_finish (if not yet started)

This captures any non-global_init users who created their cct but haven't
started up the log thread yet.  As long as common_init_finish() happens
after we have all of our config options (from the mon config or whatever),
we will log (or not log) to the right location(s).

Fixes a regression in cd6a5b9c40779956629803f222c365bdb291a169

Signed-off-by: Sage Weil <sage@redhat.com>