docker may return a empty dict at last when pull images

[Jeffrey Zhang]

$ [json.loads(line.strip()) for line in c.pull('hub.xcodest.me:5000/busybox', tag='latest', stream=True)]

[{u'stream': u'Trying to pull repository hub.xcodest.me:5000/busybox ... '},
 {u'id': u'latest', u'status': u'Pulling from busybox'},
 {u'id': u'5c5fb281b01e', u'progressDetail': {}, u'status': u'Already exists'},
 {u'id': u'fc0db02f3072', u'progressDetail': {}, u'status': u'Already exists'},
 {u'status': u'Digest: sha256:ea0265569e69ab71f42ccc228499de3c65606ddaf1658f1803679016dffc9271'},
 {u'status': u'Status: Image is up to date for hub.xcodest.me:5000/busybox:latest'},
 {}]

ansible docker module also report this issue[0]

[0] https://github.com/ansible/ansible-modules-core/issues/2043

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/263037
Committed: https://git.openstack.org/cgit/openstack/kolla/commit/?id=7fe22629aba3aad2577a8b396b638128218a1d53
Submitter: Jenkins
Branch: master

commit 7fe22629aba3aad2577a8b396b638128218a1d53
Author: Jeffrey Zhang <email address hidden>
Date: Sun Jan 3 21:38:08 2016 +0800

    Fix the docker may return a empty dict when pull images

    Closes-Bug: #1530649
    Change-Id: I74191c711d1e5c27d33011be4d5528fe08c14273