Worker threads should respond to kill command in any state

Summary:
There were some states where worker threads were not responsive to kill
command. Fixed those cases. Also added a stop slave stress test.

Reviewed By: anirbanr-fb

Differential Revision: D9073572

fbshipit-source-id: 16bc2fe

mysql-test/suite/rocksdb_rpl/t/rpl_mts_dependency_unique_key_conflicts.test

@@ -36,7 +36,7 @@ set debug_sync="now wait_for signal.reached";
 # insert
 let $wait_condition=
     select count(*)= 1 from information_schema.processlist
-      where state like 'Executing Table_map event at position%';
+      where state = 'Waiting for dependencies to be satisfied';
 source include/wait_condition.inc;
 
 select * from t1;