Add support for EL8

[optiz0r]

This module mostly works, but the config test command is incompatible with corosync version on el8. The env var is ignored, and it tries to check the actual config file, which will not exist on first run, or contain the old config when the file is to be updated (and so the wrong config gets validated).

A previous attempt to fix this in #484 is out of sync with main branch.

A replacement PR based off #484 which fixes the config sync and claims compatibility with el8 in metadata will follow.

[GertjanBijl]

Note that RHEL8 does require the knet protocol to be used, the current template is hardcoded to use udpu when unicast-addresses are defined. This can be read in https://access.redhat.com/articles/3071021. Since we pay for the HA-subscription of Red Hat, we need to comply to that configuration to get support.
Is it possible to give this some priority? RHEL9 is already released as well, and it requires knet as well.

[parryb]

RHEL7 is about to be sunset, RHEL8 is about to go into maintenance only and RHEL9 is the default choice yet this module is only supporting RHEL7? We really want to use this module with our RHEL8/9 infrastructure is there any news when it will be supported on 8 & 9?

[kenyon]

@parryb @voxpupuli is a collective of volunteers, so when someone volunteers to maintain a module is when it will be maintained.