Consolidation with CDI-PIO (develop)

Generally, this is !11 (merged) rebased onto the develop branch.

This is the first develop-based version accepted by the Buildbot of ICON: https://buildbot.dkrz.de/grid?branch=m300488/cdi-pio-2-integration

tests/pio_cksum_writer.in

 #!@SHELL@
 @USE_MPI_FALSE@exit 77
+test 'x@ENABLE_GRIB@' = xyes || exit 77
 
 pio_write_args="-p PIO_WRITER -w 4"
 mpi_task_num=8