Fix CI deployment pipeline stages
Fix CI deployment pipeline stages

- Explicitly check that the branch is `master` before tagging the build
  and deploying to Integration. This is already done by the Jenkinsfile
  helper, but this makes it more obvious that deployment only happens on
  `master`.
- Wrap the Integration deployment in a pipeline stage, since this
  definition has been removed from the `deployIntegration` helper since
  this project's Jenkinsfile was created.

alphagov/collections-publisher,alphagov/collections-publisher,alphagov/collections-publisher