gnt-cluster info uses a revised format

The code is more modular and the output is YAML-compliant.

Added function in QA that uses PyYAML to parse the command output, and QA
is updated to take advantage of it (instead of using lots of complicated
REs).

Signed-off-by: Bernardo Dal Seno <bdalseno@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>