Check non json type on glance client json_request method

This patch adds Content-Type headers for request and responses in
glance_http json_request methods based on what was discussed in a
previous patch.
(https://review.openstack.org/#/c/84454/4/tempest/tests/test_glance_http.py)
Also includes a couple of unit tests to assure the behavior.

Related to bp unit-tests

Change-Id: I570c86401f878ab8048194be252ce82d1b44f5b4
cleanup on remote_client

Remove unused get_files method.

Change-Id: I6c48a0e557602fba8a2b1931ce949af2cdd8aa8c
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"
Merge "Check non json type on glance client json_request method"
Merge "cleanup on remote_client"