Missing a key for perm 'w' in permmap (src/pybin/ceph_rest_api.py:277)
It leads to a 500 error when getting mds help info via rest api.
Changed "w" to "rw" in MonCommands.h

Fixes: #7180
Signed-off-by: Kai Zhang <kazhang2@cisco.com>
Merge pull request #1112 from kazhang/wip-7180

Fix #7180 in ceph_rest_api

Reviewed-by: Sage Weil <sage@inktank.com>