UtilityApps do not respect the BUILD_TESTING=OFF configuration flag

[gordonwatts]

Two programs in UtilityApps in the master require DDTest (test_surfaces and test_cellid_position_converter). However, if you issue a cmake command with BUILD_TESTING=OFF as an argument, the DDTest library is not built. Which means it can't be found by cmake, and the config step fails.

This needs to be surrounded by an if statement. Perhaps against BUILD_TESTING. If that is the proper variable to check, I'm happy to submit a pull request. If so, let me know what branch it should be against. Many thanks!