LU-15139 osp: block reads until the object is created

LU-15139 osp: block reads until the object is created

it's possible that remote llog can be read and written simultaneously
at recovery. for example, dtx recovery thread is fetching updates
while MDD's orphan cleanup procedure is removing orphans from PENDING.

OSP can be asked to read a just created in OSP cache object while
actual object on remote MDS hasn't been created yet. OSP should
block such reads until the creation is done.

Lustre-change: https://review.whamcloud.com/47003/
Lustre-commit: 4f2914537cc32fe89c4781bcfc87c38e3fe4419c

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I5596c791a758dd542746afd961eb1ed9c97845be
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49146
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>