Modify some comments for virt driver
Modify some comments for virt driver

some virt driver comments are based on xen or libvirt, make it
more common to other hypervisors.

Change-Id: I407f440f841a1c225f4df6312d3d4a17e2a97806

vmturbo/nova,gooddata/openstack-nova,rahulunair/nova,mahak/nova,rahulunair/nova,mahak/nova,Juniper/nova,mikalstill/nova,mikalstill/nova,gooddata/openstack-nova,jianghuaw/nova,openstack/nova,jianghuaw/nova,jianghuaw/nova,klmitch/nova,phenoxim/nova,klmitch/nova,vmturbo/nova,mikalstill/nova,klmitch/nova,Juniper/nova,Juniper/nova,klmitch/nova,gooddata/openstack-nova,mahak/nova,Juniper/nova,rahulunair/nova,openstack/nova,openstack/nova,vmturbo/nova,jianghuaw/nova,vmturbo/nova,phenoxim/nova,gooddata/openstack-nova