Return API response on service update

[hannseman]

The response contains a Warnings key that should be returned so it can be handled by the caller.

See the 200 Response documentation here: https://docs.docker.com/engine/api/v1.39/#operation/ServiceUpdate

Currently the only return value from this method is True. It can never return False (it will raise instead).

With this change checks like this on the return value will still work:

response = client.update_service(...)
if response:
  ...

But it would break backwards compatability if used like this:

response = client.update_service(...)
if response is True:
  ...

As previously stated both these checks does not make sense as the only possible return value is True.

[ulyssessouza]

LGTM

[shin-]

LGTM! We can ship the change with 4.0, and the API change won't be an issue in that case.

[hannseman]

We can ship the change with 4.0, and the API change won't be an issue in that case.

Sounds good!

@shin- and @ulyssessouza thanks for the review and merge.