DERBY-3624 testfailure in storetests/st_derby715 with ibm 1.5 on iseries machine; one deadlock message missing

Change test to check locks rather than sleep for synchronization.



git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1530696 13f79535-47bb-0310-9956-ffa450edef68