Add capm3_release_branch as an env var

This capm3__release_branch environment variable will be passed to pipeline and to
the dev-env tests below in the hierarchy to determine for which CAPM3
and IPAM branch the test should be running.

Change-Id: I6845050fcc0b0a7f16481dfe84ddb4551bb5fb4a
diff --git a/jjb/metal3/job_integration_tests.yml b/jjb/metal3/job_integration_tests.yml
index 02a782b..20a6ca2 100644
--- a/jjb/metal3/job_integration_tests.yml
+++ b/jjb/metal3/job_integration_tests.yml
@@ -54,6 +54,10 @@
         default: 'main'
         description: 'Target branch of the PR'
     - string:
+        name: capm3_release_branch
+        default: '{capm3_release_branch}'
+        description: 'The target branch of CAPM3 to be used for this test'
+    - string:
         name: IMAGE_OS
         default: '{image_os}'
         description: 'Distribution to use for the target host as well as source and target cluster. Can be ubuntu or centos'