Fixes #265 OpenMPI test launching bug

 Thanks to @amckinstry for pointing this out
 `--oversubscribed` ==> `oversubscribe`

Author: zbeekman

CMakeLists.txt

@@ -342,7 +342,7 @@ function(add_mpi_test name num_mpi_proc path)
      if ( openmpi )
        if ( N LESS 2 )
 	 set( num_mpi_proc 2 )
-	 set (test_parameters --oversubscribed)
+	 set (test_parameters --oversubscribe)
        else()
 	 set ( num_mpi_proc ${N} )
        endif()