upgrade/pacific-x/parallel: Added mds.a and mds.b

Added mds daemons so that it can create
cephFS pools and set options using
`do_set_pool()` in FSCommand.cc. Such that
we can cover corner cases like that in

https://tracker.ceph.com/issues/54263

Signed-off-by: Kamoltat <ksirivad@redhat.com>
(cherry picked from commit 1bc51f057fa80b3e34d8bac06ea22ea168fb8cf8)

Conflicts:
	qa/suites/upgrade/pacific-x/parallel/0-start.yaml
		- File doesn't exist in pacific,
		- pacific-p2p-parallel/point-to-point-upgrade.yaml
		- is already running mds, so we can delete
		- pacific-x/parallel/0-start.yaml.