CI tests use deprecated pc1 Puppet release instead of main+supported

[grant-veepshosting]

Bug description

When trying to run end-to-end tests for Pull Requests, nearly all current issues (outside of unsupported OS/versions) are due to another deprecation within the software stack - the tests are still trying to use the deprecated PC1 release of Puppet to test against instead of the mainline supported.

Eg, CentOS 7:
Tries to use http://yum.puppet.com/pc1-release-el-7.noarch.rpm
Instead of https://yum.puppetlabs.com/puppet6-release-el-7.noarch.rpm