This patch covers a few changes to get the yum test case working on ppc64le
CentOS. Specifically we needed to enable the EPEL repository on CentOS
as well as ensure some of the architecture-specific tasks use the right
set of binaries during their test.
* Modify yum/tasks/proxy.yml to usernames that expose regex bug
* Fix bad regex backref/interpolation w/yum proxy username
A yum proxy username that begins with a number was being
interpolated as part of the backref, resulting in an error:
"sre_constants.error: invalid group reference"
Closes#47797
