qemu: monitor: Add better APIs for adding of objects to qemu

qemu: monitor: Add better APIs for adding of objects to qemu

Use the new monitor command internal API to allow wrapping of the object
name and alias into the JSON props so that they don't have to be passed
out of band.

The new API also takes a double pointer so that it can be cleared when
the value is consumed so that it does not need to happen in every single
caller.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>