Use external centos7-rt if present

Depending on the environment we execute this we need different
configuration for the centos7-rt repo, like at RDO zuul ci we have to
use nodepool mirrors, this patch check for a centos7-rt repo and enables
it if it's not present just creates a default one

Change-Id: I630a399d95752b1fb1e30220a582ace8d7b97f18
Related-Bug: #1814872

elements/overcloud-compute/pre-install.d/03-centos-rt

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/bash -x
 
 if [ "${DIB_DEBUG_TRACE:-0}" -gt 0 ]; then
     set -x
@@ -7,6 +7,8 @@ set -eu
 set -o pipefail
 
 if [[ "$DISTRO_NAME" == *"centos"* ]]; then
+    current_rt_repo=$(yum repolist all|grep "centos7-rt" |awk '{print $1}'| head -n 1 || true)
+    if [[ "$current_rt_repo" == "" ]]; then
     cat << EOF > /etc/yum.repos.d/centos7-rt.repo
 [centos7-rt]
 name=CentOS 7 - Realtime
@@ -14,4 +16,7 @@ baseurl=http://mirror.centos.org/centos/7/rt/x86_64/
 enabled=1
 gpgcheck=0
 EOF
+    else
+        yum-config-manager --enable $current_rt_repo
+    fi
 fi