fix #2344: ignore cloudinit in replication check

fix #2344: ignore cloudinit in replication check

When adding a cloudinit disk it does not contain media=cdrom until it is
actually created. This means the check in check_replication fails to
detect cloudinit and it is recognized as normal disk. Then parse_volname
fails because it does not match the vm-$vmid-XYZ format. To fix this we
now check explicitly if the volname matches cloudinit and if so, return
early.

Additionally 2 small cleanups replacing cloudinit regexes with the
same check for volname matches cloudinit.

Signed-off-by: Mira Limbeck <m.limbeck@proxmox.com>