Adds infra for v3 API sample creation

Adds the required infrastructure for the v3 API sample creation.
- v3 API samples and the test cases are in their own v3 directory
- API samples from "core" are now put in their own (per plugin)
  directory rather than in the root directory
- Testcases to create api samples are now placed in individual
  files rather than one giant one. I think it makes it clearer what
  testcases we do have and avoids merge conflict pain

Adds API samples for basic servers interaction

Fix for bug in servers.py where if no extension was loaded which
extends create xml deserialization an exception would occur (fixed
here because it causes the api sample tests ported to fail).

Partially implements blueprint v3-api-unittests

Change-Id: I653af49dcc499c18f14b6e1764711a9922354069
Merge "Adds infra for v3 API sample creation"