Fix gtest-parallel-wrapper

It doesn't work when '--' is not part of the command line.
It executed "gtest-parallel gtest-parallel-wrapper.py executable_name"
instead of "gtets-parallel executable_name".

NOTRY=True
TBR=kjellander@webrtc.org
BUG=None

Review-Url: https://codereview.webrtc.org/2982133002
Cr-Commit-Position: refs/heads/master@{#19077}

tools_webrtc/gtest-parallel-wrapper.py

@@ -64,10 +64,10 @@ def CatFiles(file_list, output_file):
 
 
 def get_args_and_env():
-  if '--' not in sys.argv:
-    return sys.argv, os.environ
-
+  if '--' in sys.argv:
     argv_index = sys.argv.index('--')
+  else:
+    argv_index = len(sys.argv)
 
   gtest_parallel_args = sys.argv[1:argv_index]
   executable_args = sys.argv[argv_index + 1:]