Add RHEL8 Builder for Azure

[ferricoxide]

Addresses need for RHEL8 – but not CentOS 8-stream or other relatives – builders per #394

• Declare variable "azure_custom_managed_image_name_rhel8"
• Declare variable "azure_custom_managed_image_resource_group_name_rhel8"
• Declare source "azure-arm.base"
• Declare a shell-provisioner that tolerates SELinux not being available
• Exempts the Azure-RHEL8 build from a shell provisioner that does not tolerate SELinux not being available

[ferricoxide]

Note: the testing-environment sits behind a web proxy. Didn't (previously) think that it was a caching-proxy, but, right now, even though Packer is saying it's pulling fresh AMIgen8 content, what's executing says that it's actually pulling stale AMIgen8 content. I did a git show of the PostBuild.sh script against the remote that Packer says it's pulling fresh from: the git show shows the correct content but the manner in which PostBuild.sh is executing says that whatever Packer is pulling is stale. I think that the host from which Packer is executed transits the same proxy as the Packer build-VM, so, there shouldn't be any such differences, but, the supposition for the witnessed-behavior is all I got.

Going to try a new Packer run, tomorrow, and hope that things are a bit better behaved. If not, will need to further investigate possible sources for the seeming disconnect.

[lorengordon]

go codebuild go