LU-13668 mdt: change lock mode for lease

LU-13668 mdt: change lock mode for lease

make it PW so that lfs getstripe and open-for-read do not
interrupt replication.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I20f4bbbc4e7bf9055333aba1b8cca80aa899c664
Reviewed-on: https://review.whamcloud.com/38964
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Patrick Farrell <farr0186@gmail.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>