Simplify and fixup Ubuntu upstart usage

On at least Linux Mint, need to reload upstart configuration after
installing a salt component.

Using the upstart 'status' command to check if a config exists is
unreliable (e.g. a running job with a removed config will give an
okay status)
Add support for Linux Mint and consolidate Ubuntu derivatives

A significant number of Ubuntu derivatives are functionally
equivalent for bootstrap purposes, so use standard Ubuntu install
functions instead of creating new ones for each derivative.
Merge pull request #187 from alexvh/linux_mint

Add support for Linux Mint