First cut a new mock launcher

[Mike McLean]

Michael_E_Brown at Dell.com wrote:
> 	// elevate our privileges 
> 	if (setreuid (geteuid (), geteuid ()))
> 		error("setreuid failed: %s", strerror(errno));
> 	debug("running with uid: %d, gid: %d\n", getuid(), getgid());
> 
> Is this necessary? It seems to me like this is something that can be
> done in mock.py for the cases where it is necessary, as mock.py might
> need to know the user id of the person running mock, and so it can
> switch back to that user for writing output files.

Another option is to pass the original user in a environment variable 
(like sudo does).