Improve server metadata usability

[Brian Curtin]

Currently we can only work with compute.v2.server.Server metadata on the resource and not through the proxy. https://review.openstack.org/#/c/163639/ was an attempt at this, but even that is too heavy-handed to solve the job. Working with dictionaries via methods directly on the Server resource are an easier route. I have most of this completed already, finishing tests now.

[Brian Curtin (brian.curtin)]

https://review.openstack.org/#/c/194767/

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/242694

[OpenStack Infra (hudson-openstack)]

Change abandoned by Brian Curtin (<email address hidden>) on branch: master
Review: https://review.openstack.org/194767
Reason: going with a different approach

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/242694
Committed: https://git.openstack.org/cgit/openstack/python-openstacksdk/commit/?id=5f69213a78cb3732c29b5959659f60ff775c8794
Submitter: Jenkins
Branch: master

commit 5f69213a78cb3732c29b5959659f60ff775c8794
Author: Brian Curtin <email address hidden>
Date: Fri Nov 6 18:15:56 2015 -0600

    Better support for metadata in Compute service

    Metadata for both Servers and Images as seen from the Compute
    service is less than optimal. This approach uses a mixin class
    and allows both the Server and Image resources to leverage the
    same code, as they both work with metadata in the same way.

    Change-Id: I1d6b1f4c840d1127257244472243e4fa170baa8d
    Closes-Bug: #1467732