LU-9312 hsm: convert cdt_llog_lock to a rw semaphore

Convert struct coordinator:cdt_llog_lock from a mutex to a rw
semaphore. Add a flag to cdt_llog_process() to indicate whether a read
or write lock is needed.

Change-Id: Ie5c14d8eccda22731ad0ad9594bee7db99fe9cfd
Signed-off-by: John L. Hammond <john.hammond@intel.com>
Reviewed-on: https://review.whamcloud.com/26803


Tested-by: Jenkins
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: Quentin Bouget <quentin.bouget@cea.fr>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>