Qemu Test: pci_hotplug: Update this test case

This patch creates a series of sub functions for device add
action in different version of qemu.

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
qemu.tests.pci_hotplug: Add sub test support

This patch adds sub test support for pci_hotplug test.
So that we can use following parameters to run some
sub test scripts during hotplug test.
 * sub_type_before_plug
 * sub_type_after_plug
 * sub_type_before_unplug
 * sub_type_after_unplug

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
Acked-by: Feng Yang <fyang@redhat.com>
qemu.tests.cfg: Add config file for pci_hotplug test

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
qemu.tests.cfg: Update config for nic_hotplug test

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
Signed-off-by: Feng Yang <fyang@redhat.com>