Rename sys.config to sys.config.orig

The purpose of this change is twofold.  Firstly, this makes sure that
the user chooses an appropriate configuration.  Secondly, this separates
the configuration file currently used from the one in version control,
removing the risk that temporary local changes get committed
unintentionally.

This closes FlowForwarding/LINC-Switch#242.
Merge pull request #243 from legoscia/no-default-sys-config

Rename sys.config to sys.config.orig