Reorganize Python packages

This is in preparation of moving all tests into a separate package to
enable ease of coverage checking and testing.
diff --git a/tools/distrib/python/submit.py b/tools/distrib/python/submit.py
index a3615b3..909ba56 100755
--- a/tools/distrib/python/submit.py
+++ b/tools/distrib/python/submit.py
@@ -59,7 +59,7 @@
 
 # Move to the root directory of Python GRPC.
 pkgdir = os.path.join(os.path.dirname(os.path.abspath(__file__)),
-                      '../../../src/python/src')
+                      '../../../src/python/grpcio')
 # Remove previous distributions; they somehow confuse twine.
 try:
   shutil.rmtree(os.path.join(pkgdir, 'dist/'))