EX-8971 pcc: add lctl pcc abort command to abort attaches

EX-8971 pcc: add lctl pcc abort command to abort attaches

This patch adds a new PCC command "lctl pcc abort [--wait|-w]
[--detach|-d] $LUSTRE_MNTPT $PCCROOT".
--wait|-w: wait all in-flight attaches aborted.
--detach|-d: detach the PCC copies when scan the PCC backend.

It can be used to abort in-progress attaches for a given PCC
backend. It does not remove the PCC backend from a client.

Add sanity-pcc/test_109 to verify it.

Change-Id: Ib7152f7418aa1beb840919e98bf8de53c99b5c54
Signed-off-by: Qian Yingjin <qian@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53656
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>