Ensure yum-utils is installed before using yum-config-manager

yum-utils provides yum-config-manager but the check for yum-utils is
currently being done after the first usage of yum-config-manager, which
fails if you don't have yum-utils already installed, so move it up
before the first usage of yum-config-manager.

Putting yum-utils in files/rpms/general doesn't help since
yum-config-manager is used in stack.sh before tools/install_prereqs.sh
is called.

Closes-Bug: #1467270

Change-Id: I74996c76838b7dc50d847e3bedb2d04dc55b4431
diff --git a/stack.sh b/stack.sh
index 0d9d836..f1dc74f 100755
--- a/stack.sh
+++ b/stack.sh
@@ -263,6 +263,7 @@
 EOF
     # Enable a bootstrap repo.  It is removed after finishing
     # the epel-release installation.
+    is_package_installed yum-utils || install_package yum-utils
     sudo yum-config-manager --enable epel-bootstrap
     yum_install epel-release || \
         die $LINENO "Error installing EPEL repo, cannot continue"
@@ -270,7 +271,6 @@
     sudo rm -f /etc/yum.repos.d/epel-bootstrap.repo
 
     # ... and also optional to be enabled
-    is_package_installed yum-utils || install_package yum-utils
     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-juno/rdo-release-juno-1.noarch.rpm"}