Fix tests run in random order (#599)

* allow tests to run in random mode

* Fix random test mode for fiat-convert

* allow random test execution in persistence

* fix pep8 styling

* use "usefixtures" to prevent pylint "unused parameter" message

* add pytest-random-order to travis

freqtrade/tests/conftest.py

@@ -46,7 +46,7 @@ def get_patched_freqtradebot(mocker, config) -> FreqtradeBot:
     return FreqtradeBot(config, create_engine('sqlite://'))
 
 
-@pytest.fixture(scope="module")
+@pytest.fixture(scope="function")
 def default_conf():
     """ Returns validated configuration suitable for most tests """
     configuration = {