Existing qmp() callers do not expect a response object.  In order to
implement real QMP test cases it will be necessary to inspect the
response object.

Rename qmp() to qmp_discard_response().  Later patches will introduce a
qmp() function that returns the response object and tests that use it.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NAndreas Färber <afaerber@suse.de>