sqlite-3.6.20-1 unique constraint message

https://github.com/dotcloud/docker/issues/6551

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Merge pull request #6552 from vbatts/vbatts-gh6551

sqlite-3.6.20-1 unique constraint message