fix nova's fake virt driver plugin
fix nova's fake virt driver plugin

nova's config was changed -
now virt driver parameter needs not full path for virt driver

Change-Id: I2a32b4dee3f27efc78bd1e546a96cfbc1225b8b5

nawawi/openstack,openstack-dev/devstack,dtroyer/devstack,richliu/devstack,noironetworks/devstack,nawawi/openstack,noironetworks/devstack,dtroyer/devstack,group-policy/devstack,group-policy/devstack,openstack-dev/devstack,richliu/devstack,bswartz/devstack,bswartz/devstack