EX-8027 pcc: add --wait option for PCC detach command

EX-8027 pcc: add --wait option for PCC detach command

This patch adds "--wait" option for PCC detach command.
PCC detach with this option must wait for in-progress attach on
this file finished.
Add sanity-pcc/test_107 to verify it.

Change-Id: I63d52d514884b15a7b534d0f03deee441a12d3f1
Signed-off-by: Qian Yingjin <qian@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/52374
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>