Enable support for up to 8 corosync links

Enable support for up to 8 corosync links

add_corosync_link_properties/extract_corosync_link_args are introduced
as helpers to avoid hardcoding links in parameters=>properties on
several occasions, while still providing autocompletion with pvecm by
being seperate parameters instead of an array.

Maximum number of links is given as constant MAX_LINK_COUNT, should it
change in the future.

All necessary functions have been updated to
use the new $links array format instead of seperate $link0/$link1
parameters, and call sites changed accordingly.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>