fix #2422: allow multiple Ceph public networks

fix #2422: allow multiple Ceph public networks

Multiple public networks can be defined in the ceph.conf. The networks need to
be routed to each other.

Support handling multiple IPs for a single monitor. By default, one address from
each public network is selected for monitor creation, but, as before, it can be
overwritten with the mon-address parameter, now taking a list of addresses.

On removal, make sure the all addresses are removed from the mon_host entry in
the ceph configuration.

Originally-by: Alwin Antreich <a.antreich@proxmox.com>
[handling of multiple addresses]
Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>