Change include order for smpi tests/examples to avoid conflicts

Change include order for smpi tests/examples to avoid conflicts
This include folder is the one where our mpi.h file lives.
This file is provided by various other libraries.
When another simgrid include folder contains another mpi.h file from another library, build is broken
This trouble was seen on a freebsd system with graphviz installed, which added an include path in /usr/local/include, where there was a mpi.h file from mpich
This commit forces the one from smpi to be the first and only mpi.h file examples/tests do use