Fix benchmark.utils.get_from_manager()

* get_from_manager() method should raise exception in case of
unexisting resources. So we will be able to handle this in proper
way and avoid __getitem__ exception.

* Add rally.utils.wait_for_delete() that will update resource
unit it raise excetpion (not found).

* Use rally.utils.wait_for_delete() in all methods that delete
resources

* Add part of missing tests for benchmark.utils methods

Change-Id: If9fed2418c61de9f18023b2d2cc1fd81673d9379
Closes-Bug: #1269307