LU-81 deadlock of changelog adding vs. changelog cancelling

LU-81 deadlock of changelog adding vs. changelog cancelling

This is a workaround for the deadlock of changelog adding vs.
changelog cancelling. Changelog adding always start transaction
before acquiring the catlog lock(lgh_lock), whereas, changelog
cancelling do start transaction after holding the catlog lock.

We start transaction earlier to avoid above deadlock.

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I9647b9a559f68a27dc0d4b4885857d3cf73b5b8e
Reviewed-on: http://review.whamcloud.com/1260
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>