qemuhotplugtest: Call qemuDomainAttachDeviceLive() directly

qemuhotplugtest: Call qemuDomainAttachDeviceLive() directly

There's no reason for qemuhotplugtest to reimplement which device
attach function to call (testQemuHotplugAttach()) when
qemuDomainAttachDeviceLive() already does that. Thus, drop
testQemuHotplugAttach() and call qemuDomainAttachDeviceLive()
directly.

There's one small catch though, qemuDomainAttachDeviceLive() now
calls one monitor command more (to list all aliases). We don't
care really, because we're not testing that. Therefore, just
provide a dummy reply.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Kristina Hanicova <khanicov@redhat.com>