force cmake step to fail incase no parmetis is found

Author: pratikvn

CMakeLists.txt

@@ -376,7 +376,7 @@ if(METIS_FOUND)
     set(GINKGO_HAVE_METIS 1)
 endif()
 set(GINKGO_HAVE_PARMETIS 0)
-find_package(ParMETIS)
+find_package(ParMETIS REQUIRED)
 if(ParMETIS_FOUND)
     set(GINKGO_HAVE_PARMETIS 1)
 endif()