Enhance jck/diff/diff.sh to provide more details about the difference between two different jck

[sophia-guo]

Currently diff.sh only checks if the test subfolders (depth 2) are same or not when comparing two jcks, which helps us know if jck test targets needs to be updated or not.

A complete comparison of the test subfolders will also help us know if new tests are added or former tests are removed. Correspondingly makefile or other related files can be updated easily.