openssh: use ubuntu 14.04 as base image

Required to be able to easily install Oracle's JDK in other images.

Signed-off-by: Paul Campbell <pcampbell@kemitix.net>
browser: switch to firefox

iceweasel is only available in debian and is the debranded version of
firefox. So switching to Ubuntu we need to use firefox.

Signed-off-by: Paul Campbell <pcampbell@kemitix.net>
Merge pull request #22 from kemitix/feature/use-ubuntu-as-base

Feature/use ubuntu as base