Option for Istanbul coverage to include all source files (as opposed to only files loaded during test)

> ## Please provide us with the following information:
1. OS? Windows 7, 8 or 10. Linux (which distribution). Mac OSX (Yosemite? El Capitan?)
Any
2. Versions. Please run `ng --version`. If there's nothing outputted, please run
in a Terminal: `node --version` and paste the result here:

angular-cli: 1.0.0-beta.11-webpack.2
node: 6.2.2
os: linux x64
1. Repro steps. Was this an app that wasn't created using the CLI? What change did you
do on your code? etc.

Create an application. Test some, but not all of the source files. Generated coverage will not include files that were not loaded by the tests.
1. The log given by the failure. Normally this include a stack trace and some
more information.

N/A
1. Mention any other details that might be useful.

> ---
>
> Thanks! We'll be in touch soon.

Similar to gotwarlost/istanbul#275 and karma-runner/karma-coverage#125

一部のソースファイルだけをテストして angular-cli 1.0.0-beta.11-webpack.2 でこの動作を再現し、その後 CLI がどのように coverage を生成するかを追跡します。オプションに意図された動作について、リンクされている Istanbul と karma-coverage の issue を読みます。テストで読み込まれなかったソースファイルを coverage に任意で含められるようになれば完了です。

索引モデルが issue の本文から書いたものです。