JounralingObjectStore: journal->committed_thru after replay

It's possible that the osd stopped between when the filestore op_seq file was
updated and when the journal was trimmed.  In that case, it's possible that
on boot the journal might be full, and yet not be trimmed because
commit_start assumes there is no work to do.  Calling committed_thru on the
journal ensures that the journal matches committed_seq.

Backport: giant firefly emperor dumpling Fixes: #6756 Signed-off-by: Samuel
Just <sam.just@inktank.com> Reviewed-by: Josh Durgin
<josh.durgin@inktank.com> Reviewed-by: David Zafman
<david.zafman@inktank.com>