ctest: Display test labels in failure summary

In a complex test environment, there may be a desire to add a test
property label to indicate context. Here is one such example:

    set_property(TEST mygoofytest PROPERTY LABELS might-fail-on-config-change)

Upon looking at the failed test summary, one can quickly decide whether
the failure might be expected or not.

    198 - mygoofytest (Failed)                might-fail-on-config-change