Make sure that pool connections survive non 2xx responses

[dkropachev]

Jira: https://scylladb.atlassian.net/browse/DRIVER-742
Epic: https://scylladb.atlassian.net/browse/DRIVER-739

This tracks support for [Alternator Clients]: Make sure that pool connections survive non 2xx responses in the golang Alternator Client.

Original Jira summary: alternator-client-golang: Make sure that pool connections survive non 2xx responses

Original Jira description:

• This issue describes the work to support feature [Alternator Clients]: Make sure that pool connections survive non 2xx responses in the golang Alternator Client
• <add relevant details>