[tests] add prefix path to set mpi path

scripts/opts/minimal.opts

@@ -10,6 +10,7 @@ F77=${F77:-gfortran}
 BUILD_DIR=build-minimal
 
 CMAKE_FLAGS="
+  -DCMAKE_SYSTEM_PREFIX_PATH=\"${SYSTEM_PREFIX_PATH}\" \
   -DCMAKE_CXX_FLAGS=\"-Wall -Winit-self -O1 -g \" \
   -DCMAKE_CXX_COMPILER=\"$(which ${CXX})\" \
   -DCMAKE_C_COMPILER=\"$(which ${CC})\" \