Sahara: add API tests for job binary internals

* create/list/get/delete API tests for job binary internals were added
* "get_job_binary_internal_data" method to Sahara API client was added
* "test_job_binary_internal_get_data" test was added

Partially implements: blueprint savanna-api-tests

Change-Id: Ieaa765a1e941e5c1ac1b866099dbf966d64399b2
Merge "Sahara: add API tests for job binary internals"