Avoid calling configdata.init() in tests

It takes unnecessary time (20ms without C extensions) to initialize it over and
over again - and for some reason, it takes 20s (!) on Travis.

tests/helpers/fixtures.py

@@ -200,10 +200,16 @@ def cmdline_test(request):
     return request.param
 
 
+@pytest.fixture(scope='session')
+def configdata_init():
+    """Initialize configdata if needed."""
+    if configdata.DATA is None:
+        configdata.init()
+
+
 @pytest.fixture
-def config_stub(stubs, monkeypatch):
+def config_stub(stubs, monkeypatch, configdata_init):
     """Fixture which provides a fake config object."""
-    configdata.init()
     yaml_config = stubs.FakeYamlConfig()
 
     conf = config.Config(yaml_config=yaml_config)

tests/unit/config/test_configdata.py

@@ -31,8 +31,8 @@ from qutebrowser.utils import usertypes
 
 def test_init(config_stub):
     """Test reading the default yaml file and validating the values."""
+    # configdata.init() is called by config_stub
     config_stub.val.aliases = {}
-    configdata.init()
     assert isinstance(configdata.DATA, dict)
     assert 'ignore_case' in configdata.DATA
     for option in configdata.DATA.values():