LU-9964 llite: prevent mulitple group locks

LU-9964 llite: prevent mulitple group locks

The patch adds mutex for group lock enqueue. It also adds waiting
of group lock users on a client side for a same node. This prevents
mulitple locks on the same resource and fixes a bugs when two locks
cover the same dirty pages.

The patch adds test sanity 244b. It creates threads which
opens file, takes group lock, writes data, puts group lock, closes.
It recreates the problem when a client has two or more group locks
for a single file. This leads to a wrong behaviour for a flush etc.
osc_cache_writeback_range()) ASSERTION( hp == 0 && discard == 0 )
failed
One more test for group lock with open file and fork. It checks that
childs doesn't unlock file until the last close.

Cray-bug-id: LUS-7232
Signed-off-by: Alexander Boyko <c17825@cray.com>
Change-Id: Iaf65cf26219211b76daaa1a91eeb80092c328f2d
Reviewed-on: https://review.whamcloud.com/35791
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>