Implement IPAM driver initial placeholders

[Taku Fukushima]

libnetwork's remote IPAM driver spec defines the URI endpoints and expected responses. Kuryr should have the request handlers for the endpoints and the example responses as the placeholders as the initial step for implementing the complete IPAM driver.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/250188

[OpenStack Infra (hudson-openstack)]

Change abandoned by Taku Fukushima (<email address hidden>) on branch: master
Review: https://review.openstack.org/250188
Reason: I'm abandoning this patch because it's conflicted with https://review.openstack.org/#/c/250188/ and Vikas fixed this patch up into his patch.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Gal Sagie (<email address hidden>) on branch: master
Review: https://review.openstack.org/252796
Reason: This was copied to here:
https://review.openstack.org/#/c/255132/

[OpenStack Infra (hudson-openstack)]

Change abandoned by Gal Sagie (<email address hidden>) on branch: master
Review: https://review.openstack.org/255132

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/256205
Committed: https://git.openstack.org/cgit/openstack/kuryr/commit/?id=1fafa2c692e35890b341bbd222adb79c8bd613ba
Submitter: Jenkins
Branch: master

commit 1fafa2c692e35890b341bbd222adb79c8bd613ba
Author: Vikas Choudhary <email address hidden>
Date: Fri Dec 11 09:48:58 2015 +0530

    Add Docker pluggable IPAM implementation to Kuryr

    This patch implements libnetwork's remote IPAM driver. The following
    APIs are implemented in this patch:
        - POST /IpamDriver.GetDefaultAddressSpaces
        - POST /IpamDriver.RequestPool
        - POST /IpamDriver.ReleasePool
        - POST /IpamDriver.RequestAddress
        - POST /IpamDriver.ReleaseAddress

    Change-Id: Iaba48ded3a613fd0da2796aaff3b8816b11d515d
    Co-Authored-By: Taku Fukushima <email address hidden>
    Implements: blueprint remote-ipam-driver
    Closes-Bug: #1520080
    Related-bug: #1518249