Test files are always included in the built application

[rosen-vladimirov]

Environment Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 6.1.0
• Cross-platform modules: 6.1.0
• Android Runtime: 6.1.0
• iOS Runtime: 6.1.0
• Plugin(s):

  
  {
  "nativescript": {
  "id": "org.nativescript.app1",
  "tns-android": {
    "version": "6.1.0"
  },
  "tns-ios": {
    "version": "6.1.0"
  }
  },
  "description": "NativeScript Application",
  "license": "SEE LICENSE IN <your-license-filename>",
  "repository": "<fill-your-repository-here>",
  "dependencies": {
  "nativescript-theme-core": "~1.0.6",
  "nativescript-unit-test-runner": "^0.7.0",
  "tns-core-modules": "~6.1.0"
  },
  "devDependencies": {
  "chai": "4.2.0",
  "karma": "4.3.0",
  "karma-chai": "0.1.0",
  "karma-mocha": "1.3.0",
  "karma-nativescript-launcher": "0.4.0",
  "karma-webpack": "3.0.5",
  "mocha": "6.2.0",
  "nativescript-dev-webpack": "~1.2.0"
  },
  "gitHead": "9475c272a4c74ea6baf24d578bdf46c23a400fea",
  "readme": "NativeScript Application"
  }

 - Node.js: 10.15.3

**Describe the bug**
Files with unit tests (located in `<project dir>/<app dir>/test` are always included in the built application, no matter if `tns run` or `tns test` is executed. This increases the size of application as there might be a lot of dev dependencies included in the unit test (for example `chai`). 

**To Reproduce**
1. Create a new app: `tns create app1 --js`
2. Navigate to it: `cd app1`
3. Initialize tests, for example with `mocha` framework: `tns test init --framework mocha`
4. Open the generate example.js file and add the following line at the top: `const chai = require("chai");`  (NOTE: This step is just to show that chai will be included in the built application, you can verify only example.js in step 6)
5. Run `tns prepare android` - this should not include any test files in the `bundle.js`
6. Check the generated `bundle.js` and `vendor.js` in the platforms directory:
  * check the `bundle.js` - it shouldn't contain any reference to `example.js` file - in fact it has it
  * check the `vendor.js` - it shouldn't contain any reference to `chai` - in fact it has it.

**Expected behavior**
Unit test files and testing dependencies should be included only when `tns test <platform>` command is executed.

**Additional context**
This is working correctly in versions prior to 6.0.0.