feat(config): Add config option for browser socket timeout

[ndcornelius]

Sometimes the default timeout for the SocketIO connection attempt isn't enough. There have specifically been issues with the default value of 2000 ms when running with ChromeHeadless. Increasing the timeout value seems to solve this issue in a large number of cases.

This change makes the client timeout value a configuration option. It leaves the default as 2000 ms, but allows for modifying the value if the default is not enough for the browser and environment combination that is targeted.

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[ndcornelius]

I signed it!

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[johnjbarton]

How can we know that this change was successful?

If you set the timeout to 1ms, what do you see in a test?

[johnjbarton]

The default provided upstream in socket.io is 20000. Is there any reason we should not use this default as well?

To me, at worst the extra time will mean that, should the karma server die after launching the browser, the test will last another 18secs. That seems like a small cost for an unusual case.

[johnjbarton]

I changed the default to 20000 in PR #3103 so just change the value here.

[ndcornelius]

Done!

[johnjbarton]

Please add a sentence explaining what a user will see in the case that the timeout is too small.

[ndcornelius]

Done!

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[johnjbarton]

Thanks!