virt: Add Des help class in RFBDes.py

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.tests: Add vnc test script

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.tests.cfg: Add config file for vnc test

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
qemu.tests.vnc: Separate VNC class

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
qemu.tests.vnc: Initiate random before using it

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
qemu.tests.vnc: Update log message and docstring

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