Don't run test_clock for fixedfunction images

The fixedfunction images should have their timezone information, normally stored in /usr/share/zoneinfo explicitly excluded from install. As a result the tests to set the timezone on these images should fail, causing this test suite to fail. Explicitly exclude the test_clock tests from running on fixedfunction images.

Signed-off-by: Martyn Welch martyn.welch@collabora.com