Do not rely on 'role' value when checking other nodes via REST API (#2503)

When doing the leader race we need to check that the former primary isn't alive anymore. For that we relied on non-inclusive terms. In order to simplify future work on getting rid from all non-inclusive words we change the check to rely on a difference in format of wal/xlog field. There is only "location" for the primary and "replayed_location" + "received_location" for standbys.

In addition to that we start supporting "wal" field as well as deprecated "xlog".

Co-authored-by: Polina Bungina <[email protected]>

tests/__init__.py

@@ -50,7 +50,7 @@ def requests_get(url, **kwargs):
     if url.startswith('http://local'):
         raise urllib3.exceptions.HTTPError()
     elif ':8011/patroni' in url:
-        response.content = '{"role": "replica", "xlog": {"received_location": 0}, "tags": {}}'
+        response.content = '{"role": "replica", "wal": {"received_location": 0}, "tags": {}}'
     elif url.endswith('/members'):
         response.content = '[{}]' if url.startswith('http://error') else members
     elif url.startswith('http://exhibitor'):