The race condition mentioned in the previous commit
"Stop CMake out of source tests running on 16.04"
has also been observed with test_cmake_as_subdirectory and can presumably
happen with test_cmake_as_package and test_cmake_as_package_install as well.
So skip all of these components on Ubuntu 16.04.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>