Add the ability to use sudo during install-deps.

[madelaney]

I'd like to request the ability to have fpm-cook fork out via sudo when installing packages. Our build environment is such that we can't run as root, and we use bundler. The mix of the two makes using 'install-deps' nearly impossible.

I think the default behavior can stay as-is, but add a flag --sudo (or what have you) that allows for the use of sudo).