Add 'cooldown' for scaling policy

Since we have removed 'cooldown' from most policies, we need to add it
back to the scaling policy because it is a required property there.

Change-Id: Ic3da7c18520a13b59401f2cbdf1be915e9f8c0bf

examples/policies/scaling_policy.yaml

@@ -21,3 +21,6 @@ properties:
     # cluster size to min_size or increase cluster size to max_size
     # Default False means reject scaling request directly.
     best_effort: True
+
+    # Number of seconds before allowing the cluster to be resized again.
+    cooldown: 120

senlin/policies/scaling_policy.py

@@ -50,8 +50,10 @@ class ScalingPolicy(base.Policy):
 
     _ADJUSTMENT_KEYS = (
         ADJUSTMENT_TYPE, ADJUSTMENT_NUMBER, MIN_STEP, BEST_EFFORT,
+        COOLDOWN,
     ) = (
         'type', 'number', 'min_step', 'best_effort',
+        'cooldown',
     )
 
     properties_schema = {
@@ -88,6 +90,12 @@ class ScalingPolicy(base.Policy):
                       'cluster will break the size limitation'),
                     default=False,
                 ),
+                COOLDOWN: schema.Integer(
+                    _('Number of seconds to hold the cluster for cool-down '
+                      'before allowing cluster to be resized again.'),
+                    default=0,
+                ),
+
             }
         ),
     }
@@ -103,6 +111,7 @@ class ScalingPolicy(base.Policy):
         self.adjustment_number = adjustment[self.ADJUSTMENT_NUMBER]
         self.adjustment_min_step = adjustment[self.MIN_STEP]
         self.best_effort = adjustment[self.BEST_EFFORT]
+        self.cooldown = adjustment[self.COOLDOWN]
 
     def _calculate_adjustment_count(self, current_size):
         '''Calculate adjustment count based on current_size'''

senlin/tests/unit/policies/test_scaling_policy.py

@@ -38,6 +38,7 @@ class TestScalingPolicy(base.SenlinTestCase):
                     'number': 1,
                     'min_step': 1,
                     'best_effort': False,
+                    'cooldown': 3,
                 }
             }
         }
@@ -109,6 +110,7 @@ class TestScalingPolicy(base.SenlinTestCase):
         self.assertEqual(adjustment['number'], policy.adjustment_number)
         self.assertEqual(adjustment['min_step'], policy.adjustment_min_step)
         self.assertEqual(adjustment['best_effort'], policy.best_effort)
+        self.assertEqual(adjustment['cooldown'], policy.cooldown)
 
     def test_policy_init_default_value(self):
         self.spec['properties']['adjustment'] = {}
@@ -121,6 +123,7 @@ class TestScalingPolicy(base.SenlinTestCase):
         self.assertEqual(1, policy.adjustment_number)
         self.assertEqual(1, policy.adjustment_min_step)
         self.assertFalse(policy.best_effort)
+        self.assertEqual(0, policy.cooldown)
 
     def test_calculate_adjustment_count(self):
         adjustment = self.spec['properties']['adjustment']