argparse subnamespace: begin change from str to bool

Commit to mark last version in which 'subnamespace' is a string
indicating where a subNamespace should be stored in its parent
Namespace.

We're changing over to using a 'bool' instead, and letting the
subnamespace destination be determined by the subparser name
automatically.

I don't need a git tag for this, just a commit.

Author: jb2170