[rackspace|monitoring] adding model tests for agent_token, check, and entity; added destroy method to agent_token and check models; updated models to retrieve identity from header value 'X-Object-ID'; updated check model to take an entity object or id
Removing list_entites failure test
[rackspace|monitoring] removing bad test per @irdan
Merge branch 'model_tests' of github.com:irdan/fog into model_tests
Merge pull request #13 from irdan/model_tests

[rackspace|monitoring] Added Model Tests for agent token, checks, and entities