Add Azure guest agent plugin for cloudbase-init

Adds Azure guest agent plugin needed by the Azure metadata provider

Azure instance provisioning for cloudbase-init

Adds support for Azure metadata, instrumentation and additional plugins specific for the platform.

Change the behavior of the write_file plugin for cloudbase-init

At the moment there is no difference between the case when the encoding argument is missing and the case where it is invalid for the 'write_file' plugin for cloudconfig. These cases should also be taken care of.

Add support for Docker on Windows for nova-docker

Windows Server 2016 includes a container feature with Docker support. This blueprint addresses the portability requirements to have nova-docker running on Windows.