ceph-disk: integration tests for multipath

ceph-disk: integration tests for multipath

Add integration tests for multipath to the ceph-disk workunit, with the
following caveats:

A workaround is added (explicit call to ceph-disk activate) until the
CentOS activation bug http://tracker.ceph.com/issues/12786 is fixed.

The tests do not run on Ubuntu because of the multipath / device mapper
bug
https://bugs.launchpad.net/ubuntu/+source/multipath-tools/+bug/1488688
and it has not been tested on Debian.

http://tracker.ceph.com/issues/11881 Refs: #11881

Signed-off-by: Loic Dachary <ldachary@redhat.com>