Fixing compilation errors caused by Payload no longer being an InputSupplier

See JCLOUDS-622 and https://github.com/jclouds/jclouds/commit/80a0256c
We should close it for consistency, although `StringPayload.openStream` returns a `ByteArrayInputStream` and thus does not require `close`.  Please use `ByteStreams2.toByteArrayAndClose`.