create_queue (storage) should fail

[huguesv]

When calling create_queue with an existing queue and requesting a failure on exist, it does not throw when it should.
When calling create_queue with an existing queue, it returns True when it should return False.

See the new unit tests in test_queueservice.py:

test_create_queue_already_exist
test_create_queue_fail_on_exist

By the way, this doesn't seem to be a timing issue. Adding time.sleep(180) between the 2 calls to create_queue in those tests did not make any difference.

[huguesv]

Verified as fixed.