Use waitForRehashToComplete() instead of waitForClusterToForm() when killing a node

waitForClusterToForm() will fail if it sees too many members, see ISPN-4194
ISPN-4231 DistSyncL1FuncTest.testRemoteGetArrivesButWriteOccursBeforeRegistration random failures

Restart the cache after each method, to prevent commands from the previous
test method from interfering.

Should also fix ISPN-4133 DistSyncL1FuncTest.testNonOwnerRetrievesValueFromBackupOwnerWhileWrite