buildman: Move to absolute imports

buildman: Move to absolute imports

At present buildman sets the python path on startup so that it can access
the libraries it needs. If we convert to use absolute imports this is not
necessary.

Move buildman to use absolute imports. Also adjust moveconfig.py too since
it uses some buildman modules and cannot work without this.

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