Update the "virt_driver" to "virt_type"

more info see https://docs.openstack.org/ocata/install-guide-rdo/nova-compute-install.html#finalize-installation

Change-Id: I66c2f34a76c98b35fc2567ff6d882871a750b92e

doc/operating-kolla.rst

@@ -59,7 +59,7 @@ Then run the command to upgrade::
   counting and results in an unremovable container.
 
 .. note:: Because of system technical limitations, upgrade of a libvirt
-  container when using software emulation (``virt_driver=qemu`` in nova.conf),
+  container when using software emulation (``virt_type = qemu`` in nova.conf),
   does not work at all. This is acceptable because KVM is the recommended
   virtualization driver to use with Nova.