tell verify_dependencies to be quieter

Running anything `kitchen`-related with kitchen-docker now produces lengthy stderr output, which makes it harder to see things.

Add redirection for STDERR when running the docker binary, as now running the `docker` command outputs to STDERR (version 1.2.0).
This is addressed in a [not-yet-released commit](https://github.com/docker/docker/commit/61b129d81802e3c988cc0e67e488b24968dd748a) where the `help` command is redirected.
added gentoo support
enable ssh PasswordAuthentication

on gentoo PasswordAuthentication is disabled in the default
configuration for security reasons, we have to enable it.
added emerge and paludis support for gentoo
added missing sudo for gentoo
Merge pull request #77 from miketheman/patch-1

tell verify_dependencies to be quieter
Merge pull request #78 from tbe/master

gentoo support
merge updates