<feature request> Support for alternative commands for sudo

[rpural]

We use an alternative authentication and authorization package on our Linux hosts called "Centrify", which replaces the sudo command with a new command called "dzdo". Would it be possible to support the sudo command to use as a configuration parameter so that sudospawner could support using dzdo as the command to start the spawned servers? Or, would you suggest creating an alternate installation of sudospawner ("dzdospawner"?) instead? It appears that the only line that would need to actually change would be line 57 in spawner.py ("cmd = ['sudo', '-u', self.user.name]"), but I'm worried about potential future updates being missed if we do that. A config parameter, with a default of "sudo" would keep from having to duplicate the codebase in order to change the one line.