Fix for debian/ubuntu hold and a way to add debian src only

- modules "apt hold" handling is broken in debian stable cause files in /etc/apt/preferences.d will be silently ignored if files will be split by a blank

- add a way to add deb-src to sources.list (useful for build server like jenkins)

@wilman0 there's an extra space that's causing unit test failures.  Should be
```if param_hash[:include_deb]```