Provide a basic package for sensu.

The server currently starts without error messages (on OS X) if you also
install redis and rabbitmq-server and start their processes without any
further configuration:

$ redis-server
$ rabbitmq-server
$ sensu-server

Haven't tried much more yet, but will in a bit.

(Amended: fix whitespace and string literal formatting issues, and
superfluous dependencies created by the generator script.
Thanks the-kenny!)