devmapper: return any poolStatus() error from setupBaseImage()

Docker-DCO-1.1-Signed-off-by: Mike Snitzer <snitzer@redhat.com> (github: snitm)
devmapper: skip thin-pool checks if base image wasn't fully initialized

Docker-DCO-1.1-Signed-off-by: Mike Snitzer <snitzer@redhat.com> (github: snitm)
devmapper: fix typos relative to the thin volume type of the base image

Docker-DCO-1.1-Signed-off-by: Mike Snitzer <snitzer@redhat.com> (github: snitm)