setup: add cross compiling machine

[joaocgreis]

Currently supports Raspberry Pi 1. Based on Ubuntu 14.04.

[joaocgreis]

• grep -q ^github.com ~/.ssh/known_hosts || (ssh-keyscan -t rsa github.com >> ~/.ssh/known_hosts)

EDIT: Part of the Jenkins script.

[joaocgreis]

@nodejs/build any objections to just landing this? This has been working well enough for 2 years and should be in master. There can probably be improvements, but those can be done in other PRs.

[gibfahn]

Let's just land it

[joaocgreis]

@seishun all of those seem to have the same root cause. These scripts were developed for Ansible 1, and worked well at the time. Ansible 2 seems to have changed things: ansible/ansible@2e39661

The variables are defined in ansible-vars.yaml. The solution seems simple, just change with_items: packages to with_items: "{{packages}}". The steps for ssh keys can be removed because we now use a shared key (that is already on the machine).