Workaround possibly set HAVE_DUNE_MODULE (DUNE 2.10).

For 2.10 this is set by the *-config.cmake file to TRUE which
suddenly resulted in
```
```
appearing in config.h. As TRUE is not defined we would pretend that there
is no dune-istl and compilation would fail where we pack BlockVectors
for serialization.

cmake/Modules/OpmPackage.cmake

@@ -136,6 +136,9 @@ macro (find_opm_package module deps header lib defs prog conf)
     # since we don't have any config.h yet
     list (APPEND CMAKE_REQUIRED_DEFINITIONS ${${module}_DEFINITIONS})
     list (APPEND CMAKE_REQUIRED_DEFINITIONS ${${module}_CMD_CONFIG})
+    if(HAVE_${MODULE} STREQUAL "TRUE")
+      set(HAVE_${MODULE} "")
+    endif()
     check_cxx_source_compiles ("${prog}" HAVE_${MODULE})
     cmake_pop_check_state ()
   else()