LU-11102 ldlm: run local lock bl_ast only when necessary

LU-11102 ldlm: run local lock bl_ast only when necessary

LDLM local lock will be canceled after use, and it should only
run bl_ast if it needs to trigger Commit-on-Sharing, otherwise
if this bl_ast does nothing, it will prevent subsequent
operations to run bl_ast again, therefore Commit-on-Sharing
can't be triggered.

For example, a concurrent setattr on a striped directory and
rename under this directory:
1. setattr takes UPDATE lock of directory, but not unlock it yet
(i.e., this lock is not downgraded to COS lock).
2. a concurrent 'mv' under this directory will first getattr file by
name, this getattr will take UPDATE lock of this directory, which is
racing with setattr, but this getattr is not a distributed operation,
and the lock still has writer (by setattr), bl_ast does nothing.
3. setattr unlocks this UPDATE lock.
4. rename tries to lock UPDATE lock of this directory, but this lock
was bl_ast was run before(though nothing did), it won't run again,
rename will wait until setattr transaction commit.

To fix this, run local lock bl_ast only when it will trigger
Commit-on-Sharing.

Add sanity.sh test_415 to verify this.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Change-Id: Idae241076e7cae8fe06ae6a34481fe19c7dfd2f3
Reviewed-on: https://review.whamcloud.com/32738
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>