Lazy-spawning browsers

[unsetbit]

Currently Queen expects all autopopulators to maintain an active browser pool. This can be wasteful when Queen is using paid services (Sauce Labs or Browser Stack) and idling for long periods of time.

For example, if Queen is using browsers from Sauce, by default Sauce will shut down the browsers after 90 seconds (default timeout), Queen will interpret this as an error and ask for another browser to be spawned.

The solution may be to have an options for Queen lazy-spawn these browsers, so that the browser pool provided by autopopulators are only filled up if there are active jobs or pending jobs. This would add significant overhead to job start up time (as spawning the browsers take time), but it would prevent Queen from wasting paid browser time while idling.