[ADVISOR] stop session hangs

To repro:

• setup isngle node cluster
• load travel-sample
• start advisor session: SELECT ADVISOR({'action':'start', 'duration':'40m', 'query_count':5, 'response':'50ms'});
• run queries: 
  • SELECT airportname FROM `travel-sample` WHERE type = "airport" AND lower(city) = "grenoble" AND country = "France" ;
  • SELECT airportname FROM `travel-sample` WHERE type = "airport" AND lower(city) = "grenoble" AND country = "France" ;
  • SELECT airportname FROM `travel-sample` WHERE type = "airport" AND lower(city) = "lyon" AND country = "France" ;
  • SELECT airportname FROM `travel-sample` WHERE type = "airport" AND lower(city) = "lyon" AND country = "France" ;
  • SELECT airportname FROM `travel-sample` WHERE type = "airport" AND lower(city) = "lyon" AND country = "France" ;
  •  
• stop session: select advisor({'action':'stop', 'session':'469defc9-cad8-46ef-a528-0fd7a50a9010'});

stop session does not return

cbq> select advisor({'action':'stop', 'session':'469defc9-cad8-46ef-a528-0fd7a50a9010'})

   > ;