Why:
* Want to add a new feature to parsing of stowrc files.
* Need ability to write .stowrc files for testing without risk of
squashing existing files.
This change addresses the need by:
* Reusing logic in init_test_dirs
* init_test_dirs already creates new directory structure and overwrites
$HOME to point into /tmp.
* This commit changes init_test_dirs to point $HOME at the newly created
directory structure ($OUT_DIR) instead of /tmp.
* Grants ability to write .stowrc to $HOME without fear.
* Pointing $HOME at $OUT_DIR instead of /tmp also makes cleanup easier.
* Remove $OUT_DIR vs remove specific files in /tmp.
