prefix variables so that they do not conflict with openshift-ansible

prod.hosts

@@ -3,7 +3,7 @@
 #
 [lab:vars]
 lab_dns_suffix=itix.fr
-openshift_version=3.7
+lab_openshift_version=3.7
 
 [lab:children]
 masters

roles/openshift-prereq/tasks/main.yml

@@ -10,7 +10,7 @@
       - rhel-7-server-rpms
       - rhel-7-server-optional-rpms
       - rhel-7-server-extras-rpms
-      - rhel-7-server-ose-{{ openshift_version }}-rpms
+      - rhel-7-server-ose-{{ lab_openshift_version }}-rpms
       - rhel-7-fast-datapath-rpms # see https://access.redhat.com/solutions/3008401
     tags: rpm