DISCONNECT CON1 AND CON2
  
Problem:
The test suite/binlog/t/binlog_killed.test makes the connections
con1 and con2 but forgets to disconnect them + wait till that
operation is finished at test end.
This mistake has the potential to harm subsequent tests in
case these tests depend on the content of the processlist.
 
Solution:
Added disconnect + wait_until_disconnected.inc 
within the test cleanup.