Linux tests

I've added :penguin: Linux support for `script/grunt test`... and *now* I see that #2273 does the same thing! Whoops. I'll push this out anyway, I've made some different decisions and it might be interesting to pick and choose from each.

There are currently a small number of failures, which I've pasted into [a gist](https://gist.github.com/smashwilson/700a0e7368b85c450ec8). Attempting to build packages in parallel adds a few more.

Here are my system specs:

```
smash@winter ~/code/atom (linux-tests %=) $ uname -a
Linux winter 3.11.0-12-generic #19-Ubuntu SMP Wed Oct 9 16:20:46 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
smash@winter ~/code/atom (linux-tests %=) $ cat /etc/lsb-release 
DISTRIB_ID=LinuxMint
DISTRIB_RELEASE=16
DISTRIB_CODENAME=petra
DISTRIB_DESCRIPTION="Linux Mint 16 Petra"
smash@winter ~/code/atom (linux-tests %=) $ cat /etc/os-release 
NAME="Ubuntu"
VERSION="13.10, Saucy Salamander"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 13.10"
VERSION_ID="13.10"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
```