Push to public does not handle failed rsyncs

[jness]

Noticed a failed rsync on our Jenkins server, however the job was marked as success.

This is do to the push to public functionality not checking for a successful rsync:

 2012-11-19 22:52:17,142 (INFO) iustools.controllers.admin : pushing changes to      dl.iuscommunity.org:/exports/pub/
 ssh: connect to host dl.iuscommunity.org port 22: No route to host
 rsync: connection unexpectedly closed (0 bytes received so far) [sender]
 rsync error: unexplained error (code 255) at io.c(600) [sender=3.0.6]
 2012-11-19 22:52:17,783 (INFO) iustools.controllers.admin : appending archive to      exclude list

The code uses os.system to perform its rsync:

https://github.com/rackspace/ius-tools/blob/master/src/iustools.admin/iustools/controllers/admin.py#L130-L140

Python will return the Linux return status code on os.system,
we should check the return is a successful 0 status:

http://docs.python.org/2/library/os.html#os.system