osd/PG: skip rollforward when !transaction_applied during append_log()

osd/PG: skip rollforward when !transaction_applied during append_log()

Earlier, we did pg_log.roll_forward(&handler), when
!transaction_applied, which advanced the crt and trimmed the entries
in rollforward(). Due to this, during _merge_object_divergent_entries(),
when we tried to rollback entries, those objects were not found in the
backend, and thus we hit this bug http://tracker.ceph.com/issues/36739.

With this change, we are advancing the crt value, without deleting the
objects, so that _merge_object_divergent_entries() does not fail
because of deleted objects.

Fixes: http://tracker.ceph.com/issues/36739
Signed-off-by: Neha Ojha <nojha@redhat.com>
(cherry picked from commit 17419ee39342257f5a6f41c792e8e45a8e243720)