The vhost sockets sockets are created with qemu permission, but ovs
runs with root permission. In order to allow ovs to access vhost sockets
reducing the ovs group permission from root to qemu. This is a temprovary
workaround, until ovs fixes the permission issue. The script supports
both ovs2.6 and ovs2.7 versions.
Change-Id: I172956390c19fc9824bf7590cd48bfcf6201191b