Fix abstract adapter copy method.

The abstract adapter `copy` method wasn't expecting the correct output from `readStream`. It was attempting to use the array returned by `readStream` as a resource directly. Instead, I changed it to use the `stream` key from the result array.

Also need to check that the stream is still a resource before closing. Copying Rackspace files will fail if you don't do this because the stream is longer a resource once the copy takes place. Anyways, a good sanity check.

Fixed abstract adapter copy test to return the array output from mocked `readStream` method.