--browser-channel="chrome" is passed to all browsers if multiple are used in a test run

[bobylevd]

Use case:
I want to run all tests with all browsers, and I want to run tests with Chrome instead of Chromium
to do that I'm using a combination of run parameters like:

pytest --browser=chromium --browser=firefox -browser=webkit --browser-channel=chrome

This yields errors like:
Unsupported firefox channel "chrome"
Unsupported webkit channel "chrome"

Possible solution for that would be to check what type of browser and browser-channel are passed in launch_browser fixture
#78

[mxschmitt]

I would probably recommend you to run pytest multiple times with the correct parameters instead of running it a single time and a few parameters won't get passed over.

[mxschmitt]

Closing since it's expected to pass the channel to all the browser when it's passed a single time. We recommend to run then pytest multiple times.