SVCPLAN-851: Add custom yum_upgrade postscript can run as last postscript

[billglick]

Add the following postscripts:

• rhel_release_set - set to specific RHEL EUS version, requires use of register_rhel first
• yum_upgrade - upgrade packages via yum, then schedule reboot, mainly useful for stateful nodes not running a built os image - should be last postbootscript if used

These have been tested extensively via asd-prov01 with the cmdb-dev-alinab VM.

[billglick]

I think we need to add a method of allowing RHEL to be locked to a specific EUS version. Otherwise this postscript risks updating, as an example, a RHEL 8.4 install to the latest (e.g. 8.6), before an admin has a chance to lock the release to 8.4 EUS.

Perhaps this is yet another new, optional custom postscript that should be run before the yum_upgrade postscript. I think a rhel_eus postscript that takes a parameter with the version (e.g. 8.4) should work. And this would probably need to run before the 2 puppet postscripts.

subscription-manager release --set=8.4
  # Enable the EUS repos
  subscription-manager repos --enable=rhel-8-for-x86_64-appstream-eus-rpms
  subscription-manager repos --enable=rhel-8-for-x86_64-baseos-eus-rpms
  subscription-manager repos --enable=codeready-builder-for-rhel-8-x86_64-eus-rpms

[billglick]

I'll change rhel_eus to be rhel_release_set.

That naming matches closely to the subscription-manager release --set=8.4 that actually happens in the script.