Add initial init scripts library

This is the init library as promised in #1534.  I also updated the `hack/make/ubuntu` script to use it, and to be more generic for use in Debian too by including both the upstart and the sysvinit, and adding the official upstart check to the top (so we can use the same get.docker.io package in both Ubuntu and Debian).

/cc @mzdaniel @shykes @jpetazzo @mattdm