cephadm: create /var/run/ceph/$fsid as needed

cephadm: create /var/run/ceph/$fsid as needed

The get_container_mounts method only passed this through if it already
exists so that shell etc commands will work even when this dir isn't
present yet.  Normally the systemd unit creates it.  This may not be the
case on initial bootstrap, of even later if a deploy happens but a unit
hasn't started yet.

Precreate it during bootstrap and other times before we do a deplot so
that the unit.run command has this passed through.

Signed-off-by: Sage Weil <sage@redhat.com>