[StreamExecutor] Read dev array directly in test

Summary:
Step 2 of getting GlobalDeviceMemory to own its handle.

Use the SimpleHostPlatformDevice allocate methods to create device
arrays for tests, and check for successful copies by dereferncing the
device array handle directly because we know it is really a host
pointer.

Reviewers: jlebar

Subscribers: jprice, parallel_libs-commits

Differential Revision: https://reviews.llvm.org/D24148

llvm-svn: 280428