Don't run pkg tests on GN builders

BUG=
R=sortie@google.com

Review URL: https://codereview.chromium.org/2442703002 .

tools/bots/gn_tests.py

@@ -16,7 +16,8 @@ DART_ROOT = os.path.realpath(os.path.join(SCRIPT_DIR, '..', '..'))
 def main(argv):
   test_py = os.path.join(DART_ROOT, 'tools', 'test.py')
   build_result = subprocess.call(
-      ['python', test_py] + ['--builder-tag=no_ipv6'] + argv[1:])
+      ['python', test_py, '--builder-tag=no_ipv6', '--exclude-suite=pkg']
+      + argv[1:])
   if build_result != 0:
     return build_result
   return 0