patman: Create a module for handling patchwork

patman: Create a module for handling patchwork

At present the patchwork implementation is very simple, just consisting
of a function which calls the REST API.

We want to create a fake patchwork for use in tests. So start a new
module to encapsulate communication with the patchwork server.

Use asyncio since it is easier to handle lots of concurrent requests
from different parts of the code.

Signed-off-by: Simon Glass <sjg@chromium.org>