make process_output be able to return keep_alive timeout #1179

Job	Run time
Build Firefox (ubuntu-latest, debug)	1h 43m 2s
Build Firefox (ubuntu-latest, release)	1h 33m 49s
Build Firefox (macos-latest, debug)	1h 23m 1s
Build Firefox (macos-latest, release)	1h 35m 44s
Build Firefox (windows-latest, debug)	2h 26m 5s
Build Firefox (windows-latest, release)	2h 10m 19s
Comment on PR	7s
	10h 52m 7s

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