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

src/pio_client.c

@@ -218,8 +218,7 @@ cdiPioClientStreamDefTimestep_(stream_t *streamptr, int tsID)
 void
 cdiPioClientSetup(int *pioNamespace_)
 {
-  int pioNamespace = namespaceNew();
-  *pioNamespace_ = pioNamespace;
+  int pioNamespace = *pioNamespace_ = namespaceNew();
   int callerCDINamespace = namespaceGetActive();
   namespaceSetActive(pioNamespace);
   cdiPioSerializeSetMPI();