Add developer policy about contractual APIs

Document what APIs nova considers to be public contracts, anything not
in this list should be considered a private API.

Clarify the 'API' section to make sure its clear we are talking about
the REST API.

Change-Id: If71adc7a9d5dc1bde79f75d10e67500f6f92b81f
VMware: remove unnecessary deepcopy

The rescue and unrescue methods had an unnecessay call to deepcopy.
This code was deleted.

TrivialFix

Change-Id: I288ec4620e3d2c16ac17e4664dfb9764c357877e
VMWare: Remove unnecessery method

Method get_moref from vim_utils only calls the same method
from oslo.vmware, so remove it and replace usages by
direct usages of oslo.vmware method get_moref

Change-Id: I6b1aadc39c47dd709ae622321ab3110ee7df8803
Break out quota usage refresh code from quota_reserve()

This moves the logic out of the refresh block into a private method.

This is part of a larger series to refactor the quota_reserve method.

Partial-Bug: #1369605

Change-Id: I3cbff688c7079c112ebd4551f9b30ba2be96c98c
Merge "VMWare: Remove unnecessery method"
Merge "VMware: remove unnecessary deepcopy"
Merge "Add developer policy about contractual APIs"
Merge "Break out quota usage refresh code from quota_reserve()"