Not sure if something changed in master or not but when trying this script against a Palmetto with the latest openbmc master from a ppc64le system, it failed to reboot the system. When I manually typed "reboot" in an ssh session, it did the reboot and updated the code.
Copying palmetto-20160822184209.all.tar to remote system
{u'status': u'ok', u'message': u'200 OK', u'data': u'Deferred for mounted filesystem. reboot BMC to apply.'}
Successful update started, system reboot initiated
Collecting metadata...
Metadata collection done.
Finished: SUCCESS