Parametrize SciPy Tests via command line overrides

This uses https://github.com/hashdist/hashdist/pull/297
Fix empty string test
Fix Travis multiline munging
Merge remote-tracking branch 'origin/master' into ahmadia/parametrize_scipy_tests
Merge pull request #595 from hashdist/ahmadia/parametrize_scipy_tests

Parametrize SciPy Tests via command line overrides