Fail to build docker image

[tobe]

I have tried to build docker image with `docker build -t magnum:latest .`.
But it failed all the time. It's the problem when install the python requirements and please checkout the output.

----------------------------------------
Cleaning up...
Command /usr/bin/python -c "import setuptools, tokenize;__file__='/tmp/pip_build_root/cryptography/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-k0_QYJ-record/install-record.txt --single-version-externally-managed --compile failed with error code 1 in /tmp/pip_build_root/cryptography
Storing debug log for failure in /root/.pip/pip.log
INFO[0153] The command [/bin/sh -c pip install -r /magnum/requirements.txt] returned a non-zero code: 1

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/183964

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/183964
Committed: https://git.openstack.org/cgit/openstack/magnum/commit/?id=19aaa9edf6a43c206cd454e5a523d7c044a32075
Submitter: Jenkins
Branch: master

commit 19aaa9edf6a43c206cd454e5a523d7c044a32075
Author: Kai Qiang Wu(Kennan) <email address hidden>
Date: Mon May 18 11:11:20 2015 +0800

    Fix the docker build image issue

    The python cryptography issue, check
    http://www.123code.blogspot.com/2014/10/fixed-installing-python-cryptography.html

    The ubuntu pip issue, check
    http://stackoverflow.com/questions/27341064/how-do-i-fix-importerror-cannot-import-name-incompleteread

    Closes-Bug: #1455420
    Change-Id: I8cb78f990c08cb527ebce3fa720537b5c03eb942