use rpc Connection rather than create_connection
use rpc Connection rather than create_connection

The create_connection function in neutron.common.rpc is just an alias to
Connection. This patch switches to the later so we can remove the former
in: https://review.openstack.org/#/c/560130

Change-Id: I8f0a3f18d0fb1131fe1df581bfa4c720c0808648

openstack/networking-arista,stackforge/networking-arista,openstack/networking-arista