Unit test speed improvements (#4463)

* Unit test speed improvements

- Move from insantiating data in setUp to setUpTestData

* Update UserMixin class for API testing

* Bunch of test updates

* Further test updates

* Test fixes

* Add allowances for exchange rate server not responding

* Fixes for group role test

InvenTree/part/test_pricing.py

@@ -20,6 +20,8 @@ class PartPricingTests(InvenTreeTestCase):
     def setUp(self):
         """Setup routines"""
 
+        super().setUp()
+
         self.generate_exchange_rates()
 
         # Create a new part for performing pricing calculations
@@ -29,8 +31,6 @@ class PartPricingTests(InvenTreeTestCase):
             assembly=True
         )
 
-        return super().setUp()
-
     def create_price_breaks(self):
         """Create some price breaks for the part, in various currencies"""