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.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Id0f52b90761839399102bed825569da6bfd17864
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/47003
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>