Don't filter role deps on tags

Also, fixed a bug where the tags were being merged into the wrong
data structure (passed_vars) in _build_role_dependencies()

Fixes #6439
Fixes #5709
Fixes #6542 rewrite test string for osx compatibility
Fixes #6519 Properly handle state=absent in sysctl module
Update credentials.yml documentation and handling

Changes include:

 * Update Makefile to use credentials.yml when it exists
 * Add details on the use of the credentials.yml file to README.md.
 * Update credentials.template comments