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/test_unittest.py b/api/controller/test_unittest.py
index b5422f5..2289895 100644
--- a/api/controller/test_unittest.py
+++ b/api/controller/test_unittest.py
@@ -106,7 +106,7 @@
     failed = []
     for pi in output_msg.failed_packages:
       failed.append((pi.category, pi.package_name))
-    self.assertItemsEqual(expected, failed)
+    self.assertCountEqual(expected, failed)
 
   def testOtherBuildScriptFailure(self):
     """Test build script failure due to non-package emerge error."""