Declare playbooks for groups execution

When running group validation, the playbooks list
is not set before so we need to fix that.

Change-Id: I964508a955783b5600618d4854efe67ff06298cb

validations_libs/validation_actions.py

@@ -64,7 +64,7 @@ class ValidationActions(object):
                         ansible_cfg=None, quiet=True, workdir=None):
 
         self.log = logging.getLogger(__name__ + ".run_validations")
-
+        playbooks = []
         if playbook:
             if isinstance(playbook, list):
                 playbooks = playbook