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
Hey @zhill, looks like this test fails when the value is set to 60 and passes when it's 300. Looks like the behavior is same with AWS as well.