add convtest test-conversion-tool

I am rewriting the test-runner to be more integrated with sdc.
One thing that slows it down is opening all those test-files.
Therefor this converts them to a single json-file.
Any comments on that approach ?


There is a already a json lib used in SDC. I have to say I have no idea idea if this one is better or worse, but we should probably avoid using 2 of them by either migrating this code to the other one, or migrating the code using the other one to use that one.