Fixed Help command being ignored

[ArbaazKhan1]

Closes issue #6085

When running --help command the launcher would fail due to main only searching Client groups when args[0] was not recognized and would fall through to execMainClassName treating the keyword as a class name.

Fixed by now searching for all non-Client groups by keyword before falling back to execMainClassName, so that legacy style invocations correctly route to BaseKeywordExecutable where --help is handled.

[dlmarion]

I'm not sure that this is the correct change. Issue #6326 was created before I merged in my command changes that include a command group. I think the changes here would undo the command group lookup in some sense, and I'm not sure we want that.

I re-tested the issue noted in the original ticket, that accumulo info --help didn't print the help. Testing it now with accumulo inst info --help, it now prints the help. I wonder if this issue is no longer an issue.