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
Nodestate API test for power state set

This patch implements Nodestate API tests, to set the power state of
the node for the following power states -
1. power on
2. rebooting
3. power off

Change-Id: Icbb2719ffae772878f183c0c77c1e9d9028655c1
cleanup on remote_client

Remove unused get_files method.

Change-Id: I6c48a0e557602fba8a2b1931ce949af2cdd8aa8c
make 'server' as 'required' in server update schema

This patch make the 'server' attribute as 'required' in
server update schema (base_update_server).

This attribute is not optional in server's update API response.

Partially implements blueprint nova-api-attribute-test

Change-Id: Ibec518910597fc9e03a69d1d2bc94e719cfab0f9
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 "make 'server' as 'required' in server update schema"
Merge "Nodestate API test for power state set"
Merge "Sahara: preparations for job binary tests"
Merge "Check non json type on glance client json_request method"
Merge "cleanup on remote_client"
Merge branch 'master' of https://github.com/openstack/tempest