Fix fetcher tests
Fix fetcher tests

Previously file url was used to test the fetcher module.
To improve that and make it compatible with the progressbar in fetcher #971 use a local HTTP server to emulate HTTP downloads.
modified:   tests/test_fetcher.py

StongeEtienne/dipy,FrancoisRheaultUS/dipy,StongeEtienne/dipy,villalonreina/dipy,FrancoisRheaultUS/dipy,nilgoyyou/dipy,villalonreina/dipy,matthieudumont/dipy,matthieudumont/dipy,nilgoyyou/dipy