LU-14646 flr: write a FLR file downgrade SoM

LU-14646 flr: write a FLR file downgrade SoM

Seek over file size and write a FLR file does not change its SoM
and that makes file size incorrect.

This patch also fixes rename connect flags "pccro" to "pcc_ro"
which causes that PCC-RO related tests in sanity-pcc.sh are all
skipped.

Lustre-change: https://review.whamcloud.com/43471
Lustre-commit: f437134e80a1b320e575d774061e693042f3eb4c

Fixes: 25836ff90 ("LU-10948 mdt: New connect flag for non-open-by-fid lock")
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: I3075389721bdd40be60e9206c37f6c1bea514cce
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/44273
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>