Add support for images context semantic validation

This patch adds support for images context semantic validation, it's one
of the series patches for the bp:
https://blueprints.launchpad.net/rally/+spec/benchmark-context-semantic-validation.
It just lists images to check whether the image service is available.

Partially Implements: blueprint benchmark-context-semantic-validation

Change-Id: Iecd54dc96110e5ce592478601f3c601e4275768d
Added Sahara client

The client is required for further Sahara benchmarking.

Change-Id: Icea34148f6e505a8a8765151324c566f773f6f4e
Update Tempest Config Generator

Updated method func inside generator method
to remove self

Change-Id: I26db0295d6c1ded6c2443e390f3b9c184c6619b9
Closes-Bug:#1343294
Merge "Added Sahara client"
fixes TypeError coercing of tempfile in subunit2json.py

Closes-Bug: #1343312
Change-Id: I9d86169de7dd69311fcf1478f0708a66834d5857
Remove use of random uuid from unit tests

Closes-Bug: #1340015
Change-Id: I07eb638fc2e11c136cbd124538a5dd7ea6120978
Merge "Add support for images context semantic validation"
Merge "Remove use of random uuid from unit tests"
Added cleanup for sahara objects

This change is required befor adding any sahara benchmarks.

Change-Id: I5f35cb17cfbacdee80afc7e5c153e6acea6451bb
Set any_order to True in some unit tests

In some tested methods iteritems() is used, and order of returned items
may be different (belongs on PYTHONHASHSEED).

Change-Id: I66193b530e6f5b986f351ccba6f1a40e6d3ef5f1
Merge "Added cleanup for sahara objects"
Merge "Set any_order to True in some unit tests"
Periodic runner refactoring

  'preiodic' runner renamed to rps (runs per second).
  Extensible pool of multiprocessing.Process was implemented instead
  of using constant length multiprocessing.Pool. That should decrease memory
  usage on large iterations and related errors.

Change-Id: I6e367ea30d89d5d0e7ba212ed22e8658421ac9bd