Simplify RDO install

We can just directly install the latest RDO repo rather than having to
keep this up-to-date.  I don't think there is actually much there we
need any more; there was a lot more coming from RDO in the centos6
days.  openvswitch is one big one, however.

Change-Id: I42b8bc1aea8ff61770987eecd5fc3b8309c1e210
diff --git a/stack.sh b/stack.sh
index d8ab52e..01b1165 100755
--- a/stack.sh
+++ b/stack.sh
@@ -286,14 +286,7 @@
     # ... and also optional to be enabled
     sudo yum-config-manager --enable rhel-7-server-optional-rpms
 
-    RHEL_RDO_REPO_RPM=${RHEL7_RDO_REPO_RPM:-"https://repos.fedorapeople.org/repos/openstack/openstack-kilo/rdo-release-kilo-1.noarch.rpm"}
-    RHEL_RDO_REPO_ID=${RHEL7_RDO_REPO_ID:-"openstack-kilo"}
-
-    if ! sudo yum repolist enabled $RHEL_RDO_REPO_ID | grep -q $RHEL_RDO_REPO_ID; then
-        echo "RDO repo not detected; installing"
-        yum_install $RHEL_RDO_REPO_RPM || \
-            die $LINENO "Error installing RDO repo, cannot continue"
-    fi
+    sudo yum install -y https://rdoproject.org/repos/rdo-release.rpm
 
     if is_oraclelinux; then
         sudo yum-config-manager --enable ol7_optional_latest ol7_addons ol7_MySQL56