only() doesn't work like it does when you don't use sharding, and not documented in the readme

[ghost]

Note: for support questions, please use stackoverflow. This repository's issues are reserved for feature requests and bug reports.

• **I'm submitting a .. **

  • [ X ] bug report
  • feature request
  • support request => Please do not submit support request here, see note at the top of this template.

• Do you want to request a feature or report a bug?
  Bug:
  only() doesn't work like it does when you don't use sharding, and not documented in the readme

• What is the current behavior?
  readme says nothing about only() or how to get around it.

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via
  https://plnkr.co or similar (you can use this template as a starting point: http://plnkr.co/edit/tpl:AvJOMERrnz94ekVua0u5).

plnkr probably not needed, as this is a simple use case.

• Create 2 test files with 1 it() in each
• put only() on the it() in one of the files
• run your tests with 2 browsers

When the above is done, both tests run, one in each browser.

• What is the expected behavior?
  It should run the only() test in 1 browser and nothing in the other browser.
  Otherwise, the docs should at least warn about this issue, and maybe suggest workarounds.

• What is the motivation / use case for changing the behavior?
  Consistency of use and/or completeness of documentation.

• Please tell us about your environment:

• version: "karma-sharding": "^4.4.0",
• Browser: [ChromeHeadless]
• Language: [all]

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, gitter, etc)
  Relevant dependencies:
  "istanbul": "0.4.5",
  "karma": "2.0.0",
  "karma-chai": "0.1.0",
  "karma-chrome-launcher": "2.2.0",
  "karma-coverage": "1.1.1",
  "karma-junit-reporter": "1.2.0",
  "karma-mocha": "1.3.0",
  "karma-sharding": "^4.4.0",
  "mocha": "2.3.2",