Ensure help subcommand behaves as expected when given options and
a command as an argument to lookup.
Refactor to provide the parent parser as a default argument (using
weakref to avoid a reference cycle) so that the execute method can be
made consistent across all subcommands while still providing access to
the parent parser for the help subcommand.
Co-Authored-By: Paul Bourke <paul.bourke@oracle.com>
Change-Id: I9f7e10bbc2268d111dca7c3dbe55a87e3f057d87
7dd634a371