Fix finding Python in SpawnEnvSetupperTest #314

Job	Run time
C++ tests on macOS	4m 34s
C++ tests on Linux	1m 28s
Apache2 tests on Linux	2m 38s
Apache2 tests on macOS	2m 31s
Nginx tests on Linux	2m 45s
Nginx tests on macOS	3m 55s
Nginx dynamic module tests on Linux	1m 6s
Nginx dynamic module tests on macOS	1m 33s
Ruby tests on Linux	1m 7s
Ruby tests on macOS	1m 27s
Passenger Standalone tests on Linux	4m 0s
Passenger Standalone tests on macOS	4m 43s
Homebrew packaging tests	8m 20s
Node.js tests on Linux	16s
Node.js tests on macOS	31s
Source packaging tests	25s
	41m 19s

Provide feedback