[labels][tests] Add discretization label

test/discretization/box/CMakeLists.txt

 dune_add_test(NAME test_boxfvgeometry
               SOURCES test_boxfvgeometry.cc
               COMPILE_DEFINITIONS ENABLE_CACHING=false
-              LABELS unit)
+              LABELS unit discretization)
 
 dune_add_test(NAME test_boxfvgeometry_caching
               SOURCES test_boxfvgeometry.cc
               COMPILE_DEFINITIONS ENABLE_CACHING=true
-              LABELS unit)
+              LABELS unit discretization)
 
 #install sources
 install(FILES

test/discretization/cellcentered/tpfa/CMakeLists.txt

 dune_add_test(NAME test_tpfafvgeometry
               SOURCES test_tpfafvgeometry.cc
               COMPILE_DEFINITIONS ENABLE_CACHING=false
-              LABELS unit)
+              LABELS unit discretization)
 
 dune_add_test(NAME test_tpfafvgeometry_caching
               SOURCES test_tpfafvgeometry.cc
               COMPILE_DEFINITIONS ENABLE_CACHING=true
-              LABELS unit)
+              LABELS unit discretization)
 
 dune_add_test(NAME test_tpfafvgeometry_nonconforming
               SOURCES test_tpfafvgeometry_nonconforming.cc
               COMPILE_DEFINITIONS ENABLE_CACHING=false
               CMAKE_GUARD dune-alugrid_FOUND
-              LABELS unit)
+              LABELS unit discretization)
 
 dune_add_test(NAME test_cachedtpfafvgeometry_nonconforming
               SOURCES test_tpfafvgeometry_nonconforming.cc
               COMPILE_DEFINITIONS ENABLE_CACHING=true
               CMAKE_GUARD dune-alugrid_FOUND
-              LABELS unit)
+              LABELS unit discretization)

test/discretization/staggered/CMakeLists.txt

 dune_add_test(NAME test_staggeredfvgeometry
               SOURCES test_staggeredfvgeometry.cc
-              LABELS unit)
+              LABELS unit discretization)
 
 dune_add_test(NAME test_staggered_free_flow_geometry
               SOURCES test_staggered_free_flow_geometry.cc
-              LABELS unit)
+              LABELS unit discretization)
 
 #install sources
 install(FILES