unittests: handle some renamed assert methods

Python 3 renamed assert{ItemsEqual,RaisesRegexp,RegexpMatches} to
assert{CountEqual,RaisesRegex,Regex}.  Add our own handlers so we
can migrate our code now.

BUG=chromium:980619
TEST=`cros lint` is unchanged

Change-Id: I21cd4ce0b8ec6757422028d0228fea9e91cb2b1c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1829816
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/api/controller/api_unittest.py b/api/controller/api_unittest.py
index 34c2bca..040cd75 100644
--- a/api/controller/api_unittest.py
+++ b/api/controller/api_unittest.py
@@ -28,7 +28,7 @@
 
     api_controller.GetMethods(self.request, self.response, self.api_config)
 
-    self.assertItemsEqual(methods, [m.method for m in self.response.methods])
+    self.assertCountEqual(methods, [m.method for m in self.response.methods])
 
   def testValidateOnly(self):
     """Sanity check validate only calls only validate."""