Fix gpuupdate matrix

Fix gpuupdate matrix

1. Set GPU direct communications environment variables in update
   matrix to allow for multi-rank testing.
2. Fall back to the CPU update if PME is not fully offloaded
   in DD case and with PME-only rank (requred for GPU direct
   communications).

Change-Id: I66283a446b0cc58fd0165226b01bf58ce9ec90f1