Sylvain Joubert authored Nov 14, 2016 and Brad King committed Nov 15, 2016

When disabling BUILD_TESTING after a previous configure, the
`CTestTestfile.cmake` was left unchanged.  As a result, ctest would see
the tests while the user disabled testing.  Now when BUILD_TESTING is
OFF any existing `CTestTestfile.cmake` is removed ensuring an empty test
list.