test: add error rethrow to :read_response() in `it`

Before this patch interactive_tarantool `:read_response()` helper used
to just deserialise Lua errors as tables like `[{error = 'msg'}]`.
Now it checks if response is actually an error and rethrows it.
This provides additional verification for many tests that use
interactive_tarantool.

This patch is a followup to commit 261a21bd ("test/config: adjust
initial permissions in a test"). It provides additional output checks
to prevent similar issues.

Part of #8967

NO_DOC=test helper update
NO_CHANGELOG=test helper update
NO_TEST=test helper update