Specify device adapter for array copy in worklet tests

Rob noticed a degridation in performance in some worklet tests when ArrayCopy was added. I hypothesize that this slowdown is doing the array copy with TBB instead of serial in the serial tests. (There have been some checks in the existing code to suggest that some operations in TBB can be slower than serial.) This change forces the array copy to be on the device for which we are testing.