Enable the SCL repository for CentOS

Enable the Software Collections (SCL) repository for CentOS. This
repository includes useful software (e.g. the Go Toolset) which is not
present in the main repository.

For example, Octavia uses a Go based testing tool and its CentOS-based
jobs got broken now with the update to CentOS 7.6 which no longer
provides golang.

Change-Id: Ic68a6d6cd7da41510e624b6bea7976d9a960af98

Author: cgoncalves

stack.sh

@@ -335,6 +335,13 @@ function _install_rdo {
     # no-op on other platforms.
     sudo yum-config-manager --enable rhel-7-server-optional-rpms
 
+    # Enable the Software Collections (SCL) repository for CentOS.
+    # This repository includes useful software (e.g. the Go Toolset)
+    # which is not present in the main repository.
+    if [[ "$os_VENDOR" =~ (CentOS) ]]; then
+        yum_install centos-release-scl
+    fi
+
     if is_oraclelinux; then
         sudo yum-config-manager --enable ol7_optional_latest ol7_addons ol7_MySQL56
     fi