Add bmo_release_branch var ir JJBs for enabling CI in BMO branches

Change-Id: I7e4587b50b68f3d045d04e95a93df30e9bd99ffd
diff --git a/jjb/metal3/job_bml_main_integration_tests.yml b/jjb/metal3/job_bml_main_integration_tests.yml
index 0d80a3f..121777c 100644
--- a/jjb/metal3/job_bml_main_integration_tests.yml
+++ b/jjb/metal3/job_bml_main_integration_tests.yml
@@ -63,6 +63,10 @@
         default: 'main'
         description: 'The target branch of CAPM3 to be used for this test'
     - string:
+        name: bmo_release_branch
+        default: 'main'
+        description: 'The target branch of BMO to be used for this test'
+    - string:
         name: CAPI_VERSION
         default: 'v1beta1'
         description: 'Cluster API version.'