Add argument support to update

Currently update silently ignores arguments and updates everything.
This is especially problematic in a production environment as you can
easily accidentally update services you didn't intend to. Without
this update it is cumbersome to update a single group.
Add tests for update with gname
Remove superfluos line spacing
Print an error message for nonexistent gname

Also add support for all to be consistent with start/stop
Added a test for all
Merge pull request #311 from gmjosack/master

Add argument support to update