qa: rbd/map-snapshot-io.sh: chown rbd device stuff

This is fugly, but sudo -E doesn't work.  Fix this after we are installing
debs and the path doesn't matter anymore!

Signed-off-by: Sage Weil <sage@inktank.com>
qa: rbd/map-snapshat-io: unmap image when done

Signed-off-by: Sage Weil <sage@inktank.com>
Merge branch 'next'