add yum repos and gpg keys

etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-Debug-7

etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-Testing-7

etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7

etc/pki/rpm-gpg/RPM-GPG-KEY-xrootd

etc/yum.repos.d/CentOS-Base.repo

etc/yum.repos.d/CentOS-CR.repo

etc/yum.repos.d/CentOS-Debuginfo.repo

etc/yum.repos.d/CentOS-Media.repo

etc/yum.repos.d/CentOS-Sources.repo

etc/yum.repos.d/CentOS-Vault.repo

etc/yum.repos.d/CentOS-fasttrack.repo

etc/yum.repos.d/CentOS-x86_64-kernel.repo

etc/yum.repos.d/epel-testing.repo

etc/yum.repos.d/epel.repo

etc/yum.repos.d/xrootd-stable-slc7.repo