Add support for knet transport

[Felipe Alencastro]

Since the release of corosync 3.0 the default transport method is knet(2) and udp/udpu are still there only for backwards compatibility(3), and their maintenance is restricted to bugfixes(1).

Among the benefits of knet over udp I would highlight these three:

1: Better tolerance for small network outages(3).
 - We've had some issues multiple times, and we had to lock our machines on MAAS in order to avoid hacluster+masakari-monitors unnecessarily rebooting compute-nodes, that's an extra risk when you have nova-compute and ceph-osd on the same host.
2: Better performance and lower latencies(3).
3: Allow for multiple rings, up to 8(2-3), enables lp:1850822.
 - This would allow to have ring0 on oam-space and ring1 on internal-space, which could help with those small network hiccups

1:https://<email address hidden>/msg12806.html
2:https://people.redhat.com/ccaulfie/docs/KnetCorosync.pdf
3:https://build.clusterlabs.org/corosync/presentations/2017-Kronosnet-The-new-face-of-corosync-communications.pdf