Add keystone auth_token in context

 * Add creating keystone auth_token in context
   when task is scheduled for execution. Auth token
   is created from workbook trust_id in case Auth_enable
 * Added transforming values of task_spec and service_spec
   with YAQL and context.
 * This feature affects some unit tests, so they are fixed
 * Added unit tests

Partially implements: blueprint mistral-dataflow

Change-Id: I15794da427bfc7babbc4e3d58a90200c10a19a72
Merge "Add keystone auth_token in context"