Deploy Pharos Dashboard on changes to compose file

Deploy Pharos Dashboard on changes to compose file

Instead of deploying the dashboard when changes to any file happens,
only changes to the docker-compose.yml file should trigger a deploy.

The deployment process would then be as follows:
  - Tag pharos-tools
  - Create a patch to set the tag in 'docker-compose.yml'
  - Merge the patch
  - New version of dashboard deployed at specific tag

Change-Id: I67a6237f00b96021df24e7a79a063d31f43df5a6
Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>