add stop timeout option #304

Job	Run time
C++ tests on Linux	1m 23s
Apache2 tests on Linux	2m 22s
Apache2 tests on macOS	2m 21s
C++ tests on macOS	3m 45s
Nginx tests on Linux	2m 25s
Nginx dynamic module tests on Linux	1m 7s
Nginx tests on macOS	3m 19s
Nginx dynamic module tests on macOS	1m 4s
Ruby tests on Linux	1m 3s
Passenger Standalone tests on Linux	3m 51s
Ruby tests on macOS	1m 4s
Passenger Standalone tests on macOS	4m 16s
Homebrew packaging tests	7m 24s
Node.js tests on Linux	15s
Node.js tests on macOS	22s
Source packaging tests	31s
	36m 32s

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