virttest.qemu_vm: Add a new list for supported devices

Other test scripts can use this list directly to check
whether some device is supported by qemu binary.

This patch also moves 'has_device' function in
'make_create_command' method into VM class, so that we
can use this method out of VM class scope.

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