qa: adjust for MDSs to get deployed before verifying their availability

qa: adjust for MDSs to get deployed before verifying their availability

The check happens when some MDSs are *just* deployed by cephadm causing
jobs to fail with:

     Command failed on smithi016 with status 1: 'sudo /home/ubuntu/cephtest/cephadm \
     --image docker.io/ceph/ceph:v16.2.4 shell -c /etc/ceph/ceph.conf -k \
     /etc/ceph/ceph.client.admin.keyring --fsid 403bfcae-706b-11ec-8c32-001a4aab830c \
     -- bash -c \'ceph --format=json mds versions | jq -e ". | add == 4"\''

Fixes: http://tracker.ceph.com/issues/53857
Signed-off-by: Venky Shankar <vshankar@redhat.com>
(cherry picked from commit 8939d8c14b911e8f57a46c442e31185ce3ca5d63)