LBaaS: fix reported binary name of a loadbalancer agent

Loadbalancer agent's actual binary name differs from what it reports
to Neutron server, so need to fix:
neutron-loadbalancer-agent -> neutron-lbaas-agent

Closes-Bug: #1248222
Change-Id: Ic4e05d0258ba8eb48b96c60d69c1dbf9f27731f6