buildimage centos7 jobs are failing to fetch mirror info 404

[Marios Andreou]

The tripleo-buildimage-overcloud-full-centos7 & overcloud-hardened jobs are failing to pull packages with 404 trying to fetch repomd.xml with trace like

 2020-11-15 19:38:53.373 | Running command: ['install-packages', 'PyYAML', 'gettext']
 2020-11-15 19:38:53.373 | > Running install-packages install.
 2020-11-15 19:38:53.373 | > + yum -v -y install PyYAML gettext
 2020-11-15 19:38:53.373 | > Loading "fastestmirror" plugin
 2020-11-15 19:38:53.373 | > Loading "priorities" plugin
 2020-11-15 19:38:53.373 | > Config time: 0.009
 2020-11-15 19:38:53.373 | > Yum version: 3.4.3
 2020-11-15 19:38:53.373 | > rpmdb time: 0.000
 2020-11-15 19:38:53.373 | > Setting up Package Sacks
 2020-11-15 19:38:53.373 | > http://mirror.centos.org/centos/7/rt/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found

Examples are at [1][2][3] and this is blocking stein/train/queens check/gate queues.

[1] https://6350d29ea0552d9b896d-16024773d98de775c76d8d6d7d6dfaac.ssl.cf5.rackcdn.com/761892/5/check/tripleo-buildimage-overcloud-full-centos-7/6374f38/build.log
[2] https://cd8004f9051fa61385b6-40ec7889760df9011e4354628420e100.ssl.cf2.rackcdn.com/758510/1/check/tripleo-buildimage-overcloud-hardened-full-centos-7/9d5409b/build.log
[3] https://438c3caaa5d91a776ad4-45249728f6b1474bc3957edc637c8eb0.ssl.cf2.rackcdn.com/760905/2/check/tripleo-buildimage-overcloud-full-centos-7/30f6e65/build.log

[Marios Andreou (marios-b)]

potential fix for this from jpena @ https://review.opendev.org/#/c/762812

[Marios Andreou (marios-b)]

well... technically speaking https://bugs.launchpad.net/tripleo/+bug/1904483 should have been marked as the duplicate since it came ~10 hours after this one :) but fine