sanity: handle both \n and \\n in mirror vars

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
sanity: fix support for regex schemes in mirrors check

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
sanity: refactor mirrors checks to be more pythonic

- Use clearer variable names
- Use variable unpacking to reference elements by name rather than index
- Sacrifice a small amount of time (iterate over protocols twice per entry
  rather than once) for clarity: use readable generator expressions with any()
  rather than maintaining state.

Signed-off-by: Christopher Larson <chris_larson@mentor.com>