hipchat pipeline integration should have an option to notify only on changes

Description

The hipchat pipeline integration can either send notifications of failed builds or all builds

Proposal

Add an option to receive notifications only if the build status changes from the last run.

Links / references

Documentation blurb

(Write the start of the documentation of this feature here, include:

1. Why should someone use it; what's the underlying problem.
2. What is the solution.
3. How does someone use this

During implementation, this can then be copied and used as a starter for the documentation.)