Remove unused client from "_create_network" method
Remove unused client from "_create_network" method

routers_client is not used in this method

Change-Id: I26e972aee0137a74c9fe7c10abf291d1d5ae68cc

cisco-openstack/tempest,masayukig/tempest,Juniper/tempest,openstack/tempest,vedujoshi/tempest,openstack/tempest,cisco-openstack/tempest,Juniper/tempest,masayukig/tempest,vedujoshi/tempest