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

透過只測試部分原始碼檔案，使用 angular-cli 1.0.0-beta.11-webpack.2 重現此行為，然後追蹤 CLI 如何產生 coverage。閱讀連結的 Istanbul 與 karma-coverage issues，以了解該選項預期的行為。當 coverage 可以選擇性地包含測試未載入的原始碼檔案時，即完成。

由索引模型根據 Issue 內容生成。