LU-14397 ptlrpc: idle import vs lock enqueue race

LU-14397 ptlrpc: idle import vs lock enqueue race

There is a window after ptlrpc_check_import_is_idle()
and setting LUSTRE_IMP_CONNECTING for lock enqueue.
The lock get granted on OST and is returned to the client.
Server's lock is destroyed on OST_DISCONNECT.

Perform import counters check with setting LUSTRE_IMP_CONNECTING.
A regression test_812c was added to sanity.

HPE-bug-id: LUS-8705
Signed-off-by: Andriy Skulysh <c17819@cray.com>
Signed-off-by: Alexander Boyko <alexander.boyko@hpe.com>
Change-Id: I85da18b29ca58f811ecde8ce72ba24373388947e
Reviewed-on: https://review.whamcloud.com/41403
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Andriy Skulysh <askulysh@gmail.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>