Create: improve messages from validate_geometry.

Create: improve messages from validate_geometry.

When validate_geometry finds that we haven't committed to
a metadata yet and that the subdev is a member of 'our'
container, it needs to report any errors it finds as Create()
cannot report them effectively.

So make a slight change to the semantics of the 'verbose' flag
and allow validate_geometry to report if it printed any error
messages.

Signed-off-by: NeilBrown  <neilb@suse.de>