Move interface creation and deletion

[OpenStack Infra]

https://review.openstack.org/394547
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.
Your project "openstack/kuryr-libnetwork" is set up so that we directly report the documentation bugs against it. If this needs changing, the docimpact-group option needs to be added for the project. You can ask the OpenStack infra team (#openstack-infra on freenode) for help if you need to.

commit 56d288f5085b077ee16798ac86116126287a6a61
Author: Louise Daly <email address hidden>
Date: Tue Nov 8 06:03:45 2016 +1300

    Move interface creation and deletion

    The current implementation calls interface create/delete in
    NetworkDriver.Join/NetworkDriver.Leave but Docker has been observed to
    release the interface to the default namespace in
    NetworkDriver.DeleteEndpoint. This would suggest in order to be
    compliant with Docker Libnetwork, interface creation and deletion should
    be done in NetworkDriver.CreateEndpoint and NetworkDriver.DeleteEndpoint

    Please note that while the implementation before this patch works anyway
    for vEth pairs, it is not compatible with other interface types (e.g.
    IPVlan) as it would be impossible for Kuryr to delete the endpoint until
    Docker moves it to the default namespace

    This patch moves the current interface creation/deletion from
    NetworkDriver.Join/NetworkDriver.Leave to
    NetworkDriver.CreateEndpoint/NetworkDriver.DeleteEndpoint

    _create_or_update port was refactored to return the neutron_port and
    subnets associated with the interface_cidr, the interface_response
    message creation has been moved to NetworkDriver.CreateEndpoint

    DocImpact
    Co-Authored-By: Marco Chiappero <email address hidden>
    Change-Id: I84999989cec34a2a5b5cd2821155f150223c84cc