Remove the plugin import from auto_alloc extension
Remove the plugin import from auto_alloc extension

Currently the auto_allocated_topology extension is importing its plugin.
This patch changes it to use the Neutron Manager and remove that coupling

Change-Id: I16e3db3e7d2d676b3253d02b6adf1fa7b7065591

eayunstack/neutron,sebrandon1/neutron,mahak/neutron,openstack/neutron,mahak/neutron,huntxu/neutron,cloudbase/neutron,igor-toga/local-snat,sebrandon1/neutron,openstack/neutron,openstack/neutron,cloudbase/neutron,huntxu/neutron,mahak/neutron,eayunstack/neutron,igor-toga/local-snat,noironetworks/neutron,noironetworks/neutron