Reset filter list before running each test

Without this, in pytest,  when CFHT tests run they define a "u" filter,
and when the DECam tests run they fail because the "u" filter
has already been defined.

tests/jointcalTestBase.py

@@ -8,6 +8,7 @@
 import inspect
 
 import lsst.afw.geom
+import lsst.afw.image.utils
 from lsst.meas.extensions.astrometryNet import LoadAstrometryNetObjectsTask, LoadAstrometryNetObjectsConfig
 
 from lsst.jointcal import jointcal, utils
@@ -70,6 +71,10 @@ def setUp_base(self, center, radius,
         # Append `msg` arguments to assert failures.
         self.longMessage = True
 
+        # Ensure that the filter list is reset for each test so that we avoid
+        # confusion or contamination from other instruments.
+        lsst.afw.image.utils.resetFilters()
+
     def tearDown(self):
         if getattr(self, 'reference', None) is not None:
             del self.reference