[WIP] Support for CentOS8

[yadvr]

This adds support for CentOS8 packaging. The first would be to support CentOS8 as KVM host, and then as mgmt+usage server host.

Tasks:

• Create BO/docker container for packaging
• Test/support packaging for management and usage server, on CentOS8 host
• Test/support packaging for KVM agent, on CentOS8 KVM host
• Depends on JDK11 support #3601 (jdk changes, mysql dependency support/version)

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (improves an existing feature and functionality)
• Cleanup (Code refactoring and cleanup, that may add test cases)

[yadvr]

@andrijapanicsb cc @DaanHoogland @PaulAngus @borisstoyanov - we won't have time, moved to the next 4.15 milestone.

[NuxRo]

It would be interesting to see how this goes as CentOS8 (like Ubuntu 20.04) has switched from iptables to nftables, though the command "iptables" is still present, it's just using nftables underneath. This might impact security group functionality.

If this is the case, it might be a good occasion to check whether SG functionality can be moved entirely into libvirt.

https://libvirt.org/firewall.html

[yadvr]

Closed in favour of the new PR.