libvirt: Add test module for virsh update-device v4

I resend a patch about "virsh update-device" with commit message, and fixed up some issues.
Li Yang (1):
  libvirt: Add test module for virsh update-device

 libvirt/tests/cfg/virsh_update_device.cfg |   52 +++++++++
 libvirt/tests/virsh_update_device.py      |  177 +++++++++++++++++++++++++++++
 2 files changed, 229 insertions(+), 0 deletions(-)
 create mode 100644 libvirt/tests/cfg/virsh_update_device.cfg
 create mode 100644 libvirt/tests/virsh_update_device.py