Add performance degradation SLA plugin

This adds SLA plugin that finds minimum and maximum duration of
iterations completed without errors during Rally task execution.
Assuming that minimum duration is 100%, it calculates
performance degradation against maximum duration.

Example config:
  sla:
    performance_degradation:
      max_degradation: 75

Spec: sla_pd_plugin
Change-Id: Ieedba7be72364f5599a3c0cf79f5f494a7391ea0

doc/specs/implemented/sla_pd_plugin.rst

@@ -0,0 +1,68 @@
+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+==================================
+SLA Performance degradation plugin
+==================================
+
+Problem description
+===================
+
+During density and reliability testing of OpenStack with Rally
+we observed test cases, during execution of which performance
+of OpenStack cluster has been drammatically degradated.
+
+Proposed change
+===============
+
+Develop a new Rally SLA plugin: *performance_degradation*
+
+This SLA plugin should find minimum and maximum duration of
+iterations completed without errors during Rally task execution.
+Assuming that minimum duration is 100%, it should calculate
+performance degradation against maximum duration.
+
+SLA plugin results:
+  - failure if performance degradation is more than value set
+  in plugin's max_degradation parameter;
+  - success if degradation is less
+  - performance degradation value as a percentage.
+
+How to enable this plugin:
+
+.. code:: json
+
+    "sla": {
+        "performance_degradation": {
+            "max_degradation": 50
+            }
+    }
+
+Alternatives
+------------
+
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+
+anevenchannyy <anevenchannyy@mirantis.com>
+
+Work Items
+----------
+
+ - Implement plugin
+ - Add non-voting job with this plugin to the most important OpenStack services
+
+Dependencies
+============
+
+None

rally-jobs/rally.yaml

@@ -404,6 +404,8 @@
           max: 1
           min_iterations: 10
           sigmas: 10
+        performance_degradation:
+          max_degradation: 50
 
     -
       args:

tests/functional/test_cli_task.py

@@ -980,3 +980,50 @@ class SLAExtraFlagsTestCase(unittest.TestCase):
                                    "times": 5,
                                    "rps": 3,
                                    "timeout": 6})
+
+
+class SLAPerfDegrTestCase(unittest.TestCase):
+
+    def _get_sample_task_config(self, max_degradation=500):
+        return {
+            "Dummy.dummy_random_action": [
+                {
+                    "args": {
+                        "actions_num": 5,
+                        "sleep_min": 0.5,
+                        "sleep_max": 2
+                    },
+                    "runner": {
+                        "type": "constant",
+                        "times": 10,
+                        "concurrency": 5
+                    },
+                    "sla": {
+                        "performance_degradation": {
+                            "max_degradation": max_degradation
+                        }
+                    }
+                }
+            ]
+        }
+
+    def test_sla_fail(self):
+        rally = utils.Rally()
+        cfg = self._get_sample_task_config(max_degradation=1)
+        config = utils.TaskConfig(cfg)
+        rally("task start --task %s" % config.filename)
+        self.assertRaises(utils.RallyCliError, rally, "task sla_check")
+
+    def test_sla_success(self):
+        rally = utils.Rally()
+        config = utils.TaskConfig(self._get_sample_task_config())
+        rally("task start --task %s" % config.filename)
+        rally("task sla_check")
+        expected = [
+            {"benchmark": "Dummy.dummy_random_action",
+             "criterion": "performance_degradation",
+             "detail": mock.ANY,
+             "pos": 0, "status": "PASS"},
+        ]
+        data = rally("task sla_check --json", getjson=True)
+        self.assertEqual(expected, data)