ceph-disk: cannot run unit tests

Because ceph-disk relies on hardcoded paths. The corresponding test will
be added back when ceph-disk can run from sources.

Fixes: #7085

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #1036 from dachary/wip-7085

ceph-disk: cannot run unit tests