[ember-cli] consuming apps attempt to resolve your test in-repo addons

Currently the ember-cli addon's package.json specifies some paths in the "ember-addon" object

https://github.com/linkedin/css-blocks/blob/f1259df3ce005dda256dde6ca4933acd3f2135a7/packages/%40css-blocks/ember-cli/package.json#L72-L76

This looks like an attempt to allow [in-repo addons within this library's dummy app](https://github.com/linkedin/css-blocks/tree/09f1a176861b094c86111d6e95f53e2c2634050b/packages/%40css-blocks/ember-cli/tests/dummy/lib) to be properly resolved and [used in tests](https://github.com/linkedin/css-blocks/blob/f1259df3ce005dda256dde6ca4933acd3f2135a7/packages/%40css-blocks/ember-cli/tests/integration/template-discovery-test.js#L64-L76)

Unfortunately any consumer is going to try and potentially resolve these paths. They'll see warning messages like these

```
WARNING: The 'package.json' file for the addon at .../node_modules/@css-blocks/ember-cli
WARNING: specifies invalid, malformed or missing addons at relative paths
WARNING: 'tests/dummy/lib/in-repo-addon'
WARNING: 'tests/dummy/lib/in-repo-engine'
WARNING: 'tests/dummy/lib/in-repo-lazy-engine'
```

Version information to reproduce

```
ember-cli: 3.3.0
node: 10.11.0
os: darwin x64
yarn: 1.10.1
```
```
@css-blocks/ember-cli 0.20.0-beta.4
```

as the app attempt to resolve these three things in the `tests/dummy` folder as transitive dependencies.

What you'll want to do instead is use something like https://github.com/tomdale/ember-cli-addon-tests, which sets up a brand new app/addon/in-repo-addon/in-repo-engine [based on some fixture files](https://github.com/tomdale/ember-cli-addon-tests#fixtures). This will allow you to write similar tests to what already exist, but without running the risk of affecting consumers in any way.