rbd: fix #3969: add rbd dev paths with cluster info

By adding our own customized rbd udev rules and ceph-rbdnamer we can
create device paths that include the cluster fsid and avoid any
ambiguity if the same pool and namespace combination is used in
different clusters we connect to.

Additionally to the '/dev/rbd/<pool>/...' paths we now have
'/dev/rbd-pve/<cluster fsid>/<pool>/...' paths.

The other half of the patch makes use of the new device paths in the RBD
plugin.

The new 'get_rbd_dev_path' method the full device path. In case that the
image has been mapped before the rbd-pve udev rule has been installed,
it returns the old path.

The cluster fsid is read from the 'ceph.conf' file in the case of a
hyperconverged setup. In the case of an external Ceph cluster we need to
fetch it via a rados api call.

Co-authored-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>