Add a rule to generate .git/HEAD if it doesn't exist.
Add a rule to generate .git/HEAD if it doesn't exist.

Change-Id: I5ce7e3ab8cbfb6b6907eac1c841ceec3c6902561

MadDogTechnology/opentsdb,johann8384/opentsdb,ShefronYudy/opentsdb,OpenTSDB/opentsdb,kidaa/opentsdb,OpenTSDB/opentsdb,andyflury/opentsdb,sidhhu/opentsdb,alienth/opentsdb,OpenTSDB/opentsdb,alienth/opentsdb,johann8384/opentsdb,sidhhu/opentsdb,MadDogTechnology/opentsdb,MadDogTechnology/opentsdb,eswdd/opentsdb,kidaa/opentsdb,andyflury/opentsdb,ShefronYudy/opentsdb,eswdd/opentsdb