Add debug logs to launch daemon config

Also, fully-qualify the path to git as it was otherwise not being found
when running as root.

See "Debugging launchd jobs" at https://developer.apple.com/library/mac/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CreatingLaunchdJobs.html#//apple_ref/doc/uid/10000172i-SW7-BCIEDDBJ