[cmake][test] Cleanup build system for tests

UG and IPOpt flags are both registered via dune_register_package_flags(). Hence they need not be supplied if any of

dune_target_enable_all_packages()
dune_enable_all_packages()

is used. The dune_add_test() function, however, calls add_dune_all_flags() which is the predecessor of dune_target_enable_all_packages() and has the same effect. Hence we can drop all conditionals, lists, and loop here.

dune/solvers/test/CMakeLists.txt

-set(GRID_BASED_TESTS
-  cgsteptest
-  gssteptest
-  mmgtest
-  multigridtest
-  projectedgradienttest
-  obstacletnnmgtest
-  )
-
-set(OTHER_TESTS
-  genericvectortoolstest
-  lowrankoperatortest
-  nulloperatortest
-  sumoperatortest
-  )
-
-set(TESTS_IPOPT quadraticipoptsolvertest)
+dune_add_test(SOURCES cgsteptest.cc)
+dune_add_test(SOURCES gssteptest.cc)
+dune_add_test(SOURCES mmgtest.cc)
+dune_add_test(SOURCES multigridtest.cc)
+dune_add_test(SOURCES projectedgradienttest.cc)
+dune_add_test(SOURCES obstacletnnmgtest.cc)
+dune_add_test(SOURCES genericvectortoolstest.cc)
+dune_add_test(SOURCES lowrankoperatortest.cc)
+dune_add_test(SOURCES nulloperatortest.cc)
+dune_add_test(SOURCES sumoperatortest.cc)
 
 if(HAVE_IPOPT)
-  list(APPEND GRID_BASED_TESTS ${TESTS_IPOPT})
+    dune_add_test(SOURCES quadraticipoptsolvertest.cc)
 endif()
-
-set(TESTS ${OTHER_TESTS} ${GRID_BASED_TESTS})
-
 if(SuiteSparse_UMFPACK_FOUND)
   dune_add_test(SOURCES umfpacksolvertest.cc)
   add_dune_suitesparse_flags(umfpacksolvertest)
 endif()
-
-foreach(_test ${TESTS})
-  dune_add_test(SOURCES ${_test}.cc)
-endforeach()
-
-if(HAVE_IPOPT)
-  foreach(_test ${TESTS_IPOPT})
-    add_dune_ipopt_flags(${_test})
-  endforeach()
-endif()
-
-# Add external grid manager flags
-foreach(_test ${GRID_BASED_TESTS})
-  if(HAVE_UG)
-    add_dune_ug_flags(${_test})
-  endif(HAVE_UG)
-endforeach()