ceph-disk: unit tests

src/test/ceph-disk.sh replaces src/test/cli/ceph-disk/data-dir.t

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #1243 from dachary/wip-ceph-disk-dumpling

ceph-disk: unit tests (dumpling)

Reviewed-by: Sage Weil <sage@inktank.com>