TEST: Use the MPIEXEC variable instead of hardcoded command name. Safer on...

TEST: Use the MPIEXEC variable instead of hardcoded command name. Safer on plateforms where mpirun is not in PATH

CMake/OTBModuleTest.cmake

@@ -216,5 +216,5 @@ function(otb_add_test_mpi)
      list(APPEND ARGS ${arg})
    endforeach()
    set (test_parameters -np ${TEST_MPI_NBPROCS} ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/${TEST_MPI_COMMAND} ${ARGS})
-   otb_add_test(NAME ${TEST_MPI_NAME} COMMAND "mpirun" ${test_parameters})
+   otb_add_test(NAME ${TEST_MPI_NAME} COMMAND ${MPIEXEC} ${test_parameters})
 endfunction()