`getattr(object, 'x', object.y)` will evaluate the default argument
`object.y` regardless of whether `'x'` exists.

For details see: https://stackoverflow.com/q/31443989/770425

Previously we weren't accounting for when the response tuple also has a
`error_message` value.

Note that in Java, the error fieldname is inconsistent:
 - `CreateTopicsResponse` / `CreatePartitionsResponse` uses `topic_errors`
 - `DeleteTopicsResponse` uses `topic_error_codes`
So this updates the `CreateTopicsResponse` classes to match.

The fix is a little brittle, but should suffice for now.

`isinstance()` won't work here, as the types require identity comparison.

This was completely broken previously because it didn't lookup the group
coordinator of the consumer group. Also added basic error
handling/raising.

Note:
I added the `group_coordinator_id` as an optional kwarg. As best I
can tell, the Java client doesn't include this and instead looks it up
every time. However, if we add this, it allows the caller the
flexibility to bypass the network round trip of the lookup if for some
reason they already know the `group_coordinator_id`.

Set a clear default value for `validate_only` / `include_synonyms`

Previously the kwarg defaulted to `None`, but then sent a `False` so this
makes it more explicit and reduces ambiguity.