Build OMEC docker images with PR base branch instead of master

Change-Id: I5ff0470d6f19297dde3642fb63b7e8cd43cd811f
diff --git a/jjb/cord-macros.yaml b/jjb/cord-macros.yaml
index 5a0f123..cc12b36 100644
--- a/jjb/cord-macros.yaml
+++ b/jjb/cord-macros.yaml
@@ -151,6 +151,12 @@
                 - type: JSONPath
                   key: merged
                   value: $.pull_request.merged
+                - type: JSONPath
+                  key: branchName
+                  value: $.pull_request.base.ref
+                - type: JSONPath
+                  key: gitRef
+                  value: $.pull_request.base.ref
             regex-filter-text: $action,$merged
             regex-filter-expression: ^(closed,true)$
             cause: Generic Cause