Sahara: preparations for job binary tests

* create/list/get/delete methods to Sahara API client
  for job binaries were added
* Method "create_job_binary" was added
* tearDownClass method was expanded

Partially implements: blueprint savanna-api-tests

Change-Id: Ibac17b626008b6bfcd5ba9114b87f175a9597670
Merge "Sahara: preparations for job binary tests"