Add new action so it can use filtered data

This commit adds evacuate_vm_action which is a wrapper for nova.evacuate
API call, but it checks the result of filtering from previous step, before
executing evacuation.

Also change a little bit workflow and filter action, so they suit new
approach

Signed-off-by: Dawid Deja <dawid.deja@intel.com>

evacuate_vm_action.py

@@ -0,0 +1,17 @@
+from mistral.actions.openstack.actions import NovaAction
+from mistral.workflow.utils import Result
+
+
+class EvacuateVmAction(NovaAction):
+
+    def __init__(self, uuid, on_shared_storage, evacuate):
+        self._uuid = uuid
+        self._on_shared_storage = on_shared_storage
+        self._evacuate = evacuate
+
+    def run(self):
+        client = self._get_client()
+
+        if self._evacuate:
+            client.servers.evacuate(self._uuid,
+                                    on_shared_storage=self._on_shared_storage)