Fixes python tests where python 3.x is installed
Since #480, no default path is set so we should define one for testing python
Merged pull request: #https://github.com/jordansissel/fpm/pull/694: Fixes 2 python issues within the tests

See https://github.com/jordansissel/fpm/pull/694 for more information

* pr/694:
  Since #480, no default path is set so we should define one for testing python
  Fixes python tests where python 3.x is installed