lock.py: update keys for any owned VMs, even if none mentioned on CLI

teuthology-lock to create new VMs followed by "--list-targets" was
returning the old hostkeys.  The code rightly avoids fetching keys
for all hosts; this change makes it update keys owned by the
current querying user.

Fixes: #9871
Signed-off-by: Dan Mick <dan.mick@redhat.com>
Merge pull request #348 from ceph/wip-9871

lock.py: update keys for any owned VMs, even if none mentioned on CLI