anaconda fails if yum repo changes during installation

Issue

• Anaconda fails if a yum repo is updated with new packages and metadata while a system is installing from that repo.
  For example, if a kickstart file contains

repo --name=rhel6.1 --baseurl=http://www.example.com/rhel6.1/
repo --name=custom --baseurl=http://www.example.com/custom/
%packages
@Base
custom-pkg1
custom-pkg2
custom-pkg3

• And, while a system is installing, the admin adds or updates a new package to the custom repo and runs createrepo, Anaconda on that system will fail with:

NoMoreMirrorsRepoError: failure: repodata/filelists.sqlite.bz2 from custom: [Errno 256] No more mirrors to try.