Breaks up performance tracker tests.

The tests using performance tracker don't need the same setup
as the other performance module tests, breaking out so that
we don't call it needlessly.

tests/test_perf_tracking.py

@@ -31,7 +31,7 @@ from zipline.protocol import DATASOURCE_TYPE
 from zipline.finance.trading import TradingEnvironment
 
 
-class PerformanceTestCase(unittest.TestCase):
+class TestPerformance(unittest.TestCase):
 
     def setUp(self):
         self.onesec = datetime.timedelta(seconds=1)
@@ -536,6 +536,9 @@ shares in position"
             "should be -400 for all trades and transactions in period"
         )
 
+
+class TestPerformanceTracker(unittest.TestCase):
+
     @parameterized.expand([
         # This date range covers Columbus day,
         # however Columbus day is not a market holiday