More robust parsing of memory stats response (#3247)

Make the parsing of memory stats response more robust, to not break on
changes that will be added to the Redis server.

Also make a test related to client kill by maxage more resilient.

Co-authored-by: Gabriel Erzse <gabriel.erzse@redis.com>

Author: gerzse

tests/test_commands.py

@@ -712,7 +712,7 @@ def test_client_kill_filter_by_user(self, r, request):
     def test_client_kill_filter_by_maxage(self, r, request):
         _get_client(redis.Redis, request, flushdb=False)
         time.sleep(4)
-        assert len(r.client_list()) == 2
+        assert len(r.client_list()) >= 2
         r.client_kill_filter(maxage=2)
         assert len(r.client_list()) == 1