glcpp-test: don't return failure if valgrind tests aren't run

glcpp-test: don't return failure if valgrind tests aren't run

Success was (tests-passed AND valgrind-tests-passed) but this meant that
if the valgrind tests weren't run it would be considered a failure.

The logic is now (tests-passed AND (!valgrind OR valgrind-tests-passed))
which lets us return success if the valgrind tests aren't run.

Reviewed-by: Eric Anholt <eric@anholt.net>
Tested-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Matt Turner <mattst88@gmail.com>