LU-17685 utils: Allow nocompr flag in lfs mirror extend

LU-17685 utils: Allow nocompr flag in lfs mirror extend

Extend the set of allowed optional flags in
'lfs mirror extend' command by LCME_FL_NOCOMPR. Allowed syntax:
--flags=prefer
--flags=nocompr
--flags=prefer,nocompr

Lustre-change: https://review.whamcloud.com/54640
Lustre-commit: 37e1316050c93e5233f77ebcd399a8272b989605

Test-Parameters: trivial testlist=sanity-flr
Signed-off-by: Alexandre Ioffe <aioffe@ddn.com>
Change-Id: Id1538182eca0142464c19c0c4b1406592e615be1
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/54593
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>