tezt/agnostic_baker: automatic local mode detection

What

Tezcloud/Baker: use localhost instead of external IP when relevant

Why

Why not?

How

If node and baker are running on the same agent, use local mode.

Manually testing the MR

Run your usual teztcloud scenario. You should see bakers using --endpoint 127.0.0.1 instead of an external IP.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR