Add tag to worker job payload.
Merge branch 'master' into mm-add-tag-to-worker-payload

Conflicts:
	spec/travis/api/v2/http/request_spec.rb
	spec/travis/api/v2/http/requests_spec.rb
Add a configuration flag for the tag name.
Merge branch 'master' into mm-add-tag-to-worker-payload
Merge pull request #366 from travis-ci/mm-add-tag-to-worker-payload

Add tag to worker job payload.