Get rid of lookup utils

With the new joining mechanism lookup utils for task executions
become useless and can be removed from the codebase.
Now all requests to the database will be perforemed directly from
a workflow controller.

Action defention cache was moved to mistral/engine/actions.py,
because it's needed only there.

Change-Id: If0d4403f5c61883ecfec4cfa14b98cc39aae5618

mistral/workflow/base.py

@@ -26,7 +26,6 @@ from mistral.lang import parser as spec_parser
 from mistral import utils as u
 from mistral.workflow import commands
 from mistral.workflow import data_flow
-from mistral.workflow import lookup_utils
 from mistral.workflow import states
 
 
@@ -203,9 +202,7 @@ class WorkflowController(object):
 
         :return: True if there is one or more tasks in cancelled state.
         """
-        t_execs = lookup_utils.find_cancelled_task_executions(self.wf_ex.id)
-
-        return len(t_execs) > 0
+        return len(self._get_task_executions(state=states.CANCELLED)) > 0
 
     @abc.abstractmethod
     def evaluate_workflow_final_context(self):
@@ -252,14 +249,9 @@ class WorkflowController(object):
             return []
 
         # Add all tasks in IDLE state.
-        idle_tasks = lookup_utils.find_task_executions_with_state(
-            self.wf_ex.id,
-            states.IDLE
-        )
-
         return [
             commands.RunExistingTask(self.wf_ex, self.wf_spec, t)
-            for t in idle_tasks
+            for t in self._get_task_executions(state=states.IDLE)
         ]
 
     def _is_paused_or_completed(self):