Improved GanetiRapiClient docstrings

- Added @rtype and/or @return where missing
- Fixed @param for Query() filter_ parameter (colon was missing)

Signed-off-by: Simeon Miteff <simeon.miteff@gmail.com>
Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>