Add missing v3 token related testcases

We have added scenarios to test_check_token_existence(),
test_validate_token() and test_validate_revoke_token()

Co-Authored-By: Nishant Kumar <nk613n@att.com>
Co-Authored-By: Pramod Kumar Singh <pk110e@att.com>
Co-Authored-By: Hemanth Nakkina <nh863p@att.com>

Change-Id: I4aadd8016dc30b0fb39f22862806aeb787b3ae75
Depends-on: I0b95a19162456cbaf524ea6691e7e28c151c6ada
Closes-Bug: #1691044
4 files changed