Adapt NEMO-AGRIF to work with IOM

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main idea

We use the "swap context" functionality provided by the IO server/library. 

changes in IOIPSL code

Not specific to Agrif and not necessary needed, depends of the number of output files, but often more critical because we output more files, change in fliocom.F90  dom_max_nb=10 to a higher value.

changes in NEMO code

• add new routine iom_swap (in iom.F90) to encapsulate the call to event__swap_context, this is called at the beginning of step. The xml file is parsed only by the root grid, others iomput operations are performed by all the grids.
• the principal implication is the definition of the MPI communicator. We clean all the mess at the beginning of mynode, with AGRIF the communicator is now a shared variable between the grids and is either defined by the root grid, either transmitted by another application (OASIS, ioserver ...)
• add new routine Agrif_comm_def (in Agrif2model.F90) to transmit the ocean MPI communicator to AGRIF internal routines.

changes in AGRIF code

• change the default communicator MPI_COMM_WORLD to MPI_COMM_AGRIF, which is obtained from the model.

how to use it

There is only one iodef.xml ( no 1_iodef.xml), with the following structure:

<simulation>

<context id="nemo">

usual description of the grid, axis and data

</context>

<context id="1_nemo">

usual description of the grid, axis and data

</context>

</simulation>