entrypoint.sh: replace uses of rbd-fuse with rbd command line tool
entrypoint.sh: replace uses of rbd-fuse with rbd command line tool

Replace uses of the rbd-fuse virtual file system with command line
invocations of `rbd import` and `rbd export`. This allows us to drop
the dependency on rbd-fuse (and fuse entirely, again). Fuse requires
additional privs and special stuff so not using it makes running the
container simpler and more secure.

The only downside that I see to this change is that `rbd import` refuses
to overwrite existing images. This means the logic of the setup
function needed to be slightly changed but I don't consider it all
that different.

I did also slightly decrease the size of the image to ~500K. I didn't
think we needed to be copying so much zeros over the wire nor did
mirroring a lot of zeros demonstrate much IMO.

Signed-off-by: John Mulligan <eda8ad33169deab44f9fe65847f99e368da6c91b@redhat.com>

ceph/go-ceph,ceph/go-ceph,ceph/go-ceph