Accept Null for Identity service parameters.

[Alex Reimers]

If we pass in null as identity parameters an API error is returned. The ML2 plugin should convert these to empty strings before sending them over.

2016-09-29 16:06:08.408 INFO networking_arista.ml2.arista_ml2 [req-341a8ddd-95c2-4a16-8076-b787c34f39f8 None None] JSON request type: POST url http s://admin:arastra@172.24.18.106/openstack/api/region/Region_os_ctrl4/service-end-point data: [{"authUrl": "http://os-ctrl4.sjc.aristanetworks.com/identity/v2.0/", "password": null, "name": "keystone", "tenant": "admin", "user": null}] sync_id: None
2016-09-29 16:06:08.441 INFO networking_arista.ml2.arista_ml2 [req-341a8ddd-95c2-4a16-8076-b787c34f39f8 None None] JSON response contains: {u'error ': u"Type <type 'NoneType'> does not match API type <type 'str'>"}
2016-09-29 16:06:08.443 INFO networking_arista.ml2.arista_ml2 [req-341a8ddd-95c2-4a16-8076-

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/380460

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/380460
Committed: https://git.openstack.org/cgit/openstack/networking-arista/commit/?id=e0d51c9f31151ec3f5f0a891363a7d2c548862f7
Submitter: Jenkins
Branch: master

commit e0d51c9f31151ec3f5f0a891363a7d2c548862f7
Author: Alex Reimers <email address hidden>
Date: Fri Sep 30 10:46:27 2016 -0700

    Allow empty fields for Keystone.

    Currently if there are empty identity auth fields for Keystone we send None and the API returns an error as these fields are required. Now we convert None to the empty string, "".

    Change-Id: I6d38d4c156c67385fe83059d2ab29ea9c60ef022
    Closes-Bug: #1629405