Importing local settings will now check if pytest is active (#643)

When a user undertakes testing, for example in T3, it will import the
users local settings which can be problematic if they are not using one
of the defined ESS. Therefore, the addition of the pytest statement will
then make it so if the user is testing, it will import arcs default
settings and not the local settings.

arc/imports.py

@@ -24,7 +24,7 @@
         import settings as local_settings
     except ImportError:
         pass
-    if local_settings:
+    if local_settings and 'pytest' not in sys.modules:
         local_settings_dict = {key: val for key, val in vars(local_settings).items() if '__' not in key}
         settings.update(local_settings_dict)
         # Set global_ess_settings to None if using a local settings file (ARC's defaults are dummies)