Add jenkins-worker label to the build jenkins docker image

This will make it easier for us to use this dockerfile for integration
testing, since many jobs already use the jenkins-worker label.

docker/build/jenkins_build/ansible_overrides.yml

@@ -38,3 +38,10 @@ jenkins_common_non_plugin_template_files:
 #  - security  # intentionally left commented out
   - seed_config
 
+# Add the jenkins-worker label so that this jenkins master will work
+# out-of-the-box for running most kinds of jobs.  This makes integration
+# testing easier, and is easier for the openedx community.
+jenkins_common_main_labels:
+  - 'dsl-seed-runner'
+  - 'backup-runner'
+  - 'jenkins-worker'  # added this