Run as nobody on redhat-based systems

Provide the `--user` argument to `daemon` in the redhat init script - otherwise pystatsd runs as root. 
An empty pid file is created by root first because user `nobody` can't write to `/var/run`.

Also removed the default runlevels in the init script.  The Redhat/Fedora guidelines say that "only services which are really required for a vital system should define runlevels". See http://fedoraproject.org/wiki/Packaging:SysVInitScript#Chkconfig_Header.