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_write.c

@@ -327,9 +327,9 @@ main(int argc, char *argv[])
 
 #ifdef USE_MPI
     }
+  pioFinalize();
   namespaceSetActive(initNamespace);
   cdiPioConfDestroy(pioConfHandle);
-  pioFinalize();
   xt_finalize();
   MPI_Finalize();
 #endif