Start of Compute Behaviors refactor

* Broke create_active_server into parts: create_server_with_defaults
  and wait_for_server_creation
* Implemented StatusProgressionVerifier for server builds in
  wait_for_server_creation
* Added a base Compute behavior with a verify_entity method to handle
  basic response checks
* Removed retries for server builds
* Removed configuration for server build retries
* Fixed a minor unrelated pep8 issue in the servers behavior

Change-Id: I9cd9bb346edb76e3a5a6b72019b553884f1d18ca
Merge "Start of Compute Behaviors refactor"