SITL: add logging for x8 inputs #895

Job	Run time
build (base)	2m 59s
build (clang)	1m 59s
build-gcc-heli	2m 22s
autotest-heli (sitltest-heli)	11m 40s
autotest (sitltest-copter-tests1a)	12m 29s
autotest (sitltest-copter-tests1b)	13m 48s
autotest (sitltest-copter-tests1c)	12m 34s
autotest (sitltest-copter-tests1d)	12m 18s
autotest (sitltest-copter-tests1e)	13m 41s
autotest (sitltest-copter-tests2a)	13m 15s
autotest (sitltest-copter-tests2b)	24m 4s
	2h 1m 9s

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