Add and use a StackResourceBuildErrorException

wait_for_resource_status was raising a StackBuildErrorException with incorrect
parameters, leading to an unhelpful error message.

This will log the nova console to help diagnose Related-Bug: #1295396
Closes-Bug: #1295404

Change-Id: I979f9edcc0b57924fd3dd681b60165a3db311e6e
Add Sahara client for scenarios tests

Due to the very high load during the real life scenarios tests for
Sahara we'd like to be able to use explicitly stored scenarios tests at the
beginning.

There is a plan to add some non compute-intensive scenarios for Sahara:

* node group / cluster templates workflows;
* integration between Sahara and Swift;
* cluster provisioning tests using fake plugins to work with cirros
images.

Change-Id: I56f5b1c6528fd406f1e1b3ffef79a85aeb2ac144
Merge "Add and use a StackResourceBuildErrorException"
Merge "Add Sahara client for scenarios tests"