Bug 1614771 - Run `./mach addtest` with Python 3 r=ahal

Differential Revision: https://phabricator.services.mozilla.com/D62541

--HG--
extra : moz-landing-system : lando

mach

@@ -11,7 +11,6 @@
 # shell because `''':'`, `':'` and `:` are all equivalent, and `:` is a no-op.
 ''':'
 py2commands="
-    addtest
     analyze
     android
     android-emulator

testing/mach_commands.py

@@ -102,7 +102,7 @@ def create_parser_addtest():
     import addtest
     parser = argparse.ArgumentParser()
     parser.add_argument('--suite',
-                        choices=sorted(ADD_TEST_SUPPORTED_SUITES + SUITE_SYNONYMS.keys()),
+                        choices=sorted(ADD_TEST_SUPPORTED_SUITES + list(SUITE_SYNONYMS.keys())),
                         help='suite for the test. '
                         'If you pass a `test` argument this will be determined '
                         'based on the filename and the folder it is in')