Introduce a version cap of zhmcclient

[Markus Zoeller (markus_z)]

Description
===========
We use the master code of the zhmcclient instead of the latest stable release.
This means that we could break more easily in case the zhmcclient merges a
behavior we haven't anticipated but plans to fix it before the next stable
release is published. This is due to [1] which copies the powervm behavior [2].

Steps to reproduce
==================
    $ git clone https://github.com/openstack/nova-dpm
    $ cd nova-dpm
    $ tox -e py27
    $ .tox/py27/bin/pip show zhmcclient

Expected result
===============
It should show the latest stable release of that library. At time of this
bug report, it's version: 0.9.0

    $ .tox/py27/bin/pip show zhmcclient
    Name: zhmcclient
    Version: 0.9.0

Actual result
=============
It shows a development release based on the latest commit of the master branch.
At time of this bug report, it looks like this:

    $ .tox/py27/bin/pip show zhmcclient
    Name: zhmcclient
    Version: 0.9.1.dev2

Environment
===========
nova-dpm version:

    $ git log --oneline -1
    6f87677 Instance Destroy,poweron,poweroff,reboot

python-zhmcclient version:

    $ git log --oneline -1
    421ad4d Merge branch 'juergen/delete_completed_jobs' into 'master'

Logs & Configs
==============
N/A

References
==========
[1] https://github.com/openstack/nova-dpm/commit/00c646ab77b5e308adaaf554329be4a0af493cc8#diff-ce3c1b6e426afcb2e749638c629c0a2eR56
[2] https://github.com/openstack/nova-powervm/commit/c6d94844b850e6491b246407f9d1cd8bfed567cb

[Markus Zoeller (markus_z) (mzoeller)]

https://review.openstack.org/#/c/413689/ merges in the next hours, that should enable us to use it in the requirements.txt file like every other dependency.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/419868

[Andreas Scheuring (andreas-scheuring)]

Neutron fix: https://review.openstack.org/419836

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/419868
Committed: https://git.openstack.org/cgit/openstack/nova-dpm/commit/?id=28a7038550e5061b9a107f99d10d9ec917fd5952
Submitter: Jenkins
Branch: master

commit 28a7038550e5061b9a107f99d10d9ec917fd5952
Author: Andreas Scheuring <email address hidden>
Date: Fri Jan 13 11:05:44 2017 +0100

    Install stable zhmcclient via requirements.txt

    Till now, zhmcclient is installed from github master branch using
    pip. As zhmcclient is now an official OpenStack requirement [1]
    We can switch to install the latest stable version via
    requirements.txt.

    To allow newer versions in the future, an update to the
    upper-constraints.txt in the OpenStack requirements repo is
    required.

    To bump the minimum just increase the version in requirements.txt
    of nova-dpm and make sure, that newer versions are allowed
    by OpenStack requirements (see above).

    [1] https://review.openstack.org/413689

    Change-Id: I0da5f9271ee3391a4648064207eab5b4fb7e26fb
    Closes-Bug: #1655905