Update existing patch to write a default config

Instead of doing multipl things.  This just creates a statsd.conf with
some default values.
Patch to replce statsd bin with shell script.

This is necessary to handle the different names the nodejs binary can
have - it's /usr/bin/node on precise, and /usr/bin/nodejs on trusty.
Simplify upstart script.

This now uses the updated statsd bin.  It also uses the upstart setuid
and setgui mechanism for changing user.
New statsd package version.

Also cleanup some other bits:
* Make this `Architecture: any` as it doesn't have any compiled binaries
* Cleanup postinstall to only attempt to create user if it doesn't
  exist.
* Cleanup rules file.
Merge pull request #72 from alphagov/statsd_update

Update packaging of statsd.