Exit with statuscode 0 for repo help init

The complete help text is printed, so the program executed successfully.

Some tools (like OpenGrok) detects the availibility of a program by
running it with a known set of options and check the return code.
It is an easy and portable way of checking for the existence of a program
instead of searching the path (and handle extensions) ourselves.

Change-Id: Ic13428c77be4a36d599ccb8c86d893308818eae3