Add tools/validate_tags.py framework to automatically validate the usage
of tags in reference/projects.yaml. This is only for tags that can be
enforced pragmatically.
This is not intended for gating purposes, rather to make the process of
updating projects.yaml easier.
Supports both team and repository based tags.
Updated diversity.py to work with validate_tags
Change-Id: Id477bfcfccb4dbf5f03f328273c9487ccc48e054
bf8d72ea96