Improve replication_state=streaming check in behave (#3269)

it was somewhat flaky

features/standby_cluster.feature

@@ -13,9 +13,7 @@ Feature: standby cluster
     When I start postgres-0
     Then "members/postgres-0" key in DCS has state=running after 10 seconds
     And replication works from postgres-1 to postgres-0 after 15 seconds
-    When I issue a GET request to http://127.0.0.1:8008/patroni
-    Then I receive a response code 200
-    And I receive a response replication_state streaming
+    And Response on GET http://127.0.0.1:8008/patroni contains replication_state=streaming after 10 seconds
     And "members/postgres-0" key in DCS has replication_state=streaming after 10 seconds
 
   @slot-advance
@@ -35,9 +33,7 @@ Feature: standby cluster
     Then postgres-1 is a leader of batman1 after 10 seconds
     When I add the table foo to postgres-0
     Then table foo is present on postgres-1 after 20 seconds
-    When I issue a GET request to http://127.0.0.1:8009/patroni
-    Then I receive a response code 200
-    And I receive a response replication_state streaming
+    And Response on GET http://127.0.0.1:8009/patroni contains replication_state=streaming after 10 seconds
     And I sleep for 3 seconds
     When I issue a GET request to http://127.0.0.1:8009/primary
     Then I receive a response code 503
@@ -49,9 +45,7 @@ Feature: standby cluster
     Then postgres-2 role is the replica after 24 seconds
     And postgres-2 is replicating from postgres-1 after 10 seconds
     And table foo is present on postgres-2 after 20 seconds
-    When I issue a GET request to http://127.0.0.1:8010/patroni
-    Then I receive a response code 200
-    And I receive a response replication_state streaming
+    And Response on GET http://127.0.0.1:8010/patroni contains replication_state=streaming after 10 seconds
     And postgres-1 does not have a replication slot named test_logical
 
   Scenario: check switchover

features/steps/patroni_api.py

@@ -160,9 +160,24 @@ def check_http_response(context, url, value, timeout, negate=False):
     if context.certfile:
         url = url.replace('http://', 'https://')
     timeout *= context.timeout_multiplier
+    if '=' in value:
+        key, val = value.split('=', 1)
+    else:
+        key, val = value, None
     for _ in range(int(timeout)):
         r = context.request_executor.request('GET', url)
-        if (value in r.data.decode('utf-8')) != negate:
+        data = r.data.decode('utf-8')
+        if val is not None:
+            try:
+                data = json.loads(data)
+                if negate:
+                    if key not in data or data[key] != val:
+                        break
+                elif key in data and data[key] == val:
+                    break
+            except Exception:
+                pass
+        elif (value in r.data.decode('utf-8')) != negate:
             break
         time.sleep(1)
     else: