factor out corosync methods to own module

factor out corosync methods to own module

PVE::Cluster is already quite big, the corosync part is ~250 lines
long of 1900 total. Further the corosync part is only needed in a few
specialised places (API2/ClusterConfig and CLI/pvecm).
This speaks for factoring out this part in a separate perl module as
most modules which use Cluster load the corosync parts for no reason.
Further, cluster handling through API may even add more corosync
related methods.

Create a new Corosync perl module and move all relevant methods over.
Method names lost the 'corosync_' prefix, not really needed anymore
as they already lives in the 'Corosync' namespace now.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>