Apart from using qmp() in the qmp_discard_response() macro, these
tests do not have any dependencies to the global_qtest variable,
so we can simply get rid of it here by replacing the qmp() with
qtest_qmp() in the macro.
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NThomas Huth <thuth@redhat.com>