OSD: FileJournal: call writeq_cond.Signal if necessary in submit_entry

Signed-off-by: Xinze Chi <xmdxcxz@gmail.com>
Merge pull request #3133 from XinzeChi/wip-2

OSD: FileJournal: call writeq_cond.Signal if necessary in submit_entry

Reviewed-by: Sage Weil <sage@redhat.com>
Reviewed-by: Samuel Just <sjust@redhat.com>