Add network-scripts-openvswitch2.15 as dependency for rdo-openvswitch
    
    After adding openstack-network-scripts as a dependency we can restore
    dependency on network-scripts-openvswitch2.15 which depends on
    network-scripts. This restore the existing behavior in CS8.
    
    Related-to: https://review.rdoproject.org/r/q/I7380181f5f92ce8cfb8ef3caac408d38ed2b8d49