When testing under Valgrind for constant flow, skip test suites that don't
have any constant-flow annotations, since the testing wouldn't do anything
more that testing with ordinary Valgrind (component_test_valgrind and
component_test_valgrind_psa). This is a significant time saving since
testing with Valgrind is very slow.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>