This reverts commit 7bafae1f.

The semantic is changed slightly: before GPI-2 is initialized, the output
goes to stdin. If GPI-2 is initialized, it goes to the logger.

Must stop the device before releasing and unregistering buffers.
Moves the unregistration to device (IB).

No distinction between master and worker devices.
Tied to gaspi_connect and context_connect instead of building everything at start.
No waiting for topology build.