Actually use UG

I only just now noticed that none of the tests in question was testing
anything for me. Both Alugrid and UG are considered acceptable grid
providers but if neither is viewed as found in the test (be it because
you really don't have them installed or because the build system doesn't
pass on the information properly (fixed!)), then the tests pass without
testing anything.

std::cout and std::cerr output from the individual tests is discarded by
the make test routine, so it's not trivial to warn the user (or rather
developer) about this.

dune/solvers/test/CMakeLists.txt

-set(TESTS
+set(GRID_BASED_TESTS
   cgsteptest
+  multigridtest
+  projectedgradienttest
+  obstacletnnmgtest
+  )
+
+set(OTHER_TESTS
   genericvectortoolstest
   lowrankoperatortest
-  multigridtest
   nulloperatortest
-  obstacletnnmgtest
-  projectedgradienttest
   sumoperatortest
   )
 
 set(TESTS_IPOPT mmgtest quadraticipoptsolvertest)
 
 if(HAVE_IPOPT)
-  list(APPEND TESTS ${TESTS_IPOPT})
+  list(APPEND GRID_BASED_TESTS ${TESTS_IPOPT})
 endif()
 
+set(TESTS ${OTHER_TESTS} ${GRID_BASED_TESTS})
+
 foreach(_test ${TESTS})
   add_executable(${_test} EXCLUDE_FROM_ALL ${_test}.cc)
   target_link_dune_default_libraries(${_test})
@@ -27,5 +32,12 @@ if(HAVE_IPOPT)
   endforeach()
 endif()
 
+# Add external grid manager flags
+foreach(_test ${GRID_BASED_TESTS})
+  if(HAVE_UG)
+    add_dune_ug_flags(${_test})
+  endif(HAVE_UG)
+endforeach()
+
 add_directory_test_target(_test_target)
 add_dependencies(${_test_target} ${TESTS})