more debugging
PGLog: trim mod_desc after appending to the log

We'll want he callers up the chain to take the log
entry as a const ref.

Signed-off-by: Samuel Just <sjust@redhat.com>
PG::add_log_entry: no need to 0 offset in append_log

No longer used.

Signed-off-by: Samuel Just <sjust@redhat.com>
osd/: pass log_entries in write path as const ref

We need to use them after the submit_transaction call, so
we can't pass them by non-const ref.

Signed-off-by: Samuel Just <sjust@redhat.com>