Auto merge of #1892 - kzys:fastboot-add-deps, r=carols10cents

Add Fastboot dependencies without enabling them

Fastboot-related dependencies are added by the following "npm install"
commands:

* npm i --save fastboot-app-server
* npm i --save-dev ember-cli-fastboot

But Fastboot itself is disabled by having FASTBOOT_DISABLED=true.

Author: bors