Adds presigned url tests for each verb and for sts tokens

Adds presigned_url tests for s3 api. Cherry-picked from a 'testing' based branch. Conflicts were just the list of tests, resolved the conflict manually.

Conflicts:
	testcases/cloud_user/s3/object_tests.py
I'll re-run on my setup and see if something is broken in the test. It should work with any value in the future. I don't think there is a minimum value acceptable for 'expires'.