Don't treat command termination due '-h' option as a fatal error

Don't treat command termination due '-h' option as a fatal error

Signal early command termination due '-h' or '--help' option via
TerminatedByHelpException. This allows tests using
CLIGitCommand differentiate between unexpected command parsing errors
and expected command cancellation "on help" (which also allows
validation of expected/unexpected help messages).

Additional side-effect: jgit supports now git style of handling help
option: any unexpected command line options before help are reported as
errors, but after help ignored.

Bug: 484951
Change-Id: If45c41c0d32895ab6822a7ff9d851877dcef5771
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>