ceph-conf: flush log on exit

This makes it deterministic whether we output

2014-08-03 20:59:45.482614 4036c80 -1 did not load config file, using default settings.

or not, and will make the unit tests stop intermittently failing.

Signed-off-by: Sage Weil <sage@redhat.com>
Merge pull request #2193 from ceph/wip-ceph-conf

ceph-conf: flush log on exit

Reviewed-by: Loic Dachary <loic@dachary.org>