Create a setup.py script

This will enable third party tools outside of AOSP to take a dependency
on acloud.

Change-Id: I9fce92b0112e11a46978eb626ce0a95bd07456af
Test: virtualenv env && source env/bin/activate &&
      python setup.py install && acloud --help
diff --git a/public/acloud_main.py b/public/acloud_main.py
index bc392e7..cca92c2 100644
--- a/public/acloud_main.py
+++ b/public/acloud_main.py
@@ -352,7 +352,7 @@
         logger.addHandler(fhandler)
 
 
-def main(argv):
+def main(argv=None):
     """Main entry.
 
     Args:
@@ -361,6 +361,9 @@
     Returns:
         0 if success. None-zero if fails.
     """
+    if argv is None:
+        argv = sys.argv[1:]
+
     args = _ParseArgs(argv)
     _SetupLogging(args.log_file, args.verbose)
     _VerifyArgs(args)