Setting proper OpenVDB library version

There seems to be incompatibility with the OpenVDB v9 libraries.
For now at least set the OpenVDB library to version 8 in CMake
configuration to avoid issues.

IO/OpenVDB/CMakeLists.txt

@@ -6,7 +6,13 @@ mark_as_advanced(OpenVDB_CMAKE_PATH)
 
 list(INSERT CMAKE_MODULE_PATH 0
   "${OpenVDB_CMAKE_PATH}")
-vtk_module_find_package(PACKAGE OpenVDB)
+vtk_module_find_package(PACKAGE OpenVDB VERSION 8)
+
+STRING(REGEX MATCH "[0-9]*" OpenVDB_MAJOR_VERSION ${OpenVDB_VERSION})
+
+if (NOT ${OpenVDB_MAJOR_VERSION} STREQUAL "8")
+  message(ERROR " OpenVDB needs to be major version 8 but is version ${OpenVDB_VERSION}")
+endif()
 
 set(classes
   vtkOpenVDBWriter)