Port server_diagnostics extension to v3 API Part1

This changeset only copies the v2 files (implementation and test)
into the appropriate v3 directories unchanged. The copy as-is
will not be loaded by either the v2 or v3 extension loaders. The
second changeset will then make the changes required for it to
work as a v3 extension.

This is being done in order to make reviewing of extension porting
easier as gerrit will display only what is actually changed for v3
rather than entirely new files

Implements blueprint nova-v3-api

Change-Id: I52f906948b5873cf3fdfff14270c7384ee5e7b9f
Merge "Port server_diagnostics extension to v3 API Part1"