extra_vars and image_name parametrization added to build images Jenkins jobs

Change-Id: I047d0a48cb329da972f7dcb2f03c5870bbe380a2
diff --git a/jenkins/client/job/image/centos.yml b/jenkins/client/job/image/centos.yml
index d478ccc..d5856e4 100644
--- a/jenkins/client/job/image/centos.yml
+++ b/jenkins/client/job/image/centos.yml
@@ -72,3 +72,9 @@
             OPENSTACK_API_CLIENT:
               type: string
               default: ""
+            IMAGE_NAME:
+              type: string
+              default: centos-7-x64
+            EXTRA_VARIABLES:
+              type: text
+              default: ""
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