EX-5936 pcc: dont take UPDATE lock when set lustre.pin xattr

EX-5936 pcc: dont take UPDATE lock when set lustre.pin xattr

In this patch, we do not take UPDATE lock whan set lustre.pin
XATTR during the PCC pin command.
The reason is that it may revoke the combined UPDATE|LAYOUT lock
cached on the client namespace, and invalidate the layout and PCC
cache.

As we disable to cache lustre.pin xattr on the client XATTR cache,
so it does not cause problem without taking UPDATE lock bit during
set lustre.pin XATTR.

Add test case: sanity-pcc/204d.

Change-Id: I35a0e399294020efdb0e4710500e8f7b846c290f
Signed-off-by: Qian Yingjin <qian@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/48638
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>