Refactor Network API

Base network API class to have all the methods that can be implemented
by specific network api's.

 * Move common logic and decorators to network/base_api.py
 * Base class base_api.NetworkAPI with current methods from
   nova & neutron, that will raise NotImplementedError()
 * Refactor some tests with mock

When this get merged, every review adding new methods to neutron or
nova network, must have the same methods added to the base NetworkAPI.

Implements: bp refactor-network-api

Change-Id: Ia507e80dfd1e0b7552c5d50e84ac9e642ca8c9fe
Remove mention of nova-manage.conf from nova-manage.rst

As of commit 07ee9639 three years ago nova-manage.conf is no longer
used, so let's clean up the man page.

Closes-Bug: #1304580

Change-Id: Ie061733da4bd0337f510e17b6dd7ca5bae14b7de
Xen: Do not resize root volumes

Boot from volume on Xen wants to resize the volume
when the image size doesn't jive with the volume size.
This patch doesn't attempt the resize.

Closes-Bug: #1296839
Change-Id: Ic03b7997f61f1a22362dafd86664db681e54087e
Merge "Remove mention of nova-manage.conf from nova-manage.rst"
Merge "Xen: Do not resize root volumes"
Merge "Refactor Network API"