Medium: Filesystem: allow to force cloning for local mounts

If you want to run a cluster filesystem like GlusterFS or RADOS/Ceph,
you may also want to have the underlying local filesystem on each node
under cluster control.

For very good reasons local filesystems like ext3/4 or xfs are not
allowed to be mounted on different nodes at the same time, from the
same block device - it may be a shared block device, that allows
concurrent access.

In case of a cluster filesystem setup, where we know for sure that
every node has an exclusive and local block device with a local
filesystem it is valid to allow cloning of such a filesystem
resource. This avoids the need of an extra resource definition
for every node serving parts of a distributed filesystem.

This feature is disabled per default. It is up to the user
to make sure it is safe to enable it for a particular resource!