Cover Rally with docstrings & Test this coverage

Rally should have detailed docstrings for:
* Benchmark scenario classes
* Benchmark scenarios
* Deploy engines
* Server providers
* SLA

Here we add such docstrings and also add a test suite that checks
that Rally is 100% covered with docstrings and that these docstrings
are correctly formed.

We also change the interface of the following benchmark scenarios
(for the sake of unification):
* CinderVolumes.create_and_attach_volume
* CinderVolumes.create_snapshot_and_attach_volume
* CinderVolumes.create_nested_snapshots_and_attach_volume

Finally, we refactor a bit NovaServers.boot_and_bounce_server.

Change-Id: Ia38c8fc2d692a09719d3e068d332647d4b0da47f

rally-jobs/plugins/fake_plugin.py

@@ -21,6 +21,7 @@ from rally.benchmark.scenarios import base
 
 
 class FakePlugin(base.Scenario):
+    """Fake plugin with a scenario."""
 
     @base.atomic_action_timer("test1")
     def _test1(self, factor):
@@ -32,5 +33,9 @@ class FakePlugin(base.Scenario):
 
     @base.scenario()
     def testplugin(self, factor=1):
+        """Fake scenario.
+
+        :param factor: influences the argument value for a time.sleep() call
+        """
         self._test1(factor)
         self._test2(factor)

rally-jobs/rally.yaml

@@ -734,7 +734,7 @@
   CinderVolumes.create_and_attach_volume:
     -
       args:
-        volume_size: 1
+        size: 1
         image:
           name: "^cirros.*uec$"
         flavor:
@@ -755,7 +755,7 @@
     -
       args:
           volume_type: false
-          volume_size:
+          size:
               min: 1
               max: 2
       runner:
@@ -778,7 +778,7 @@
     -
       args:
           volume_type: true
-          volume_size:
+          size:
               min: 1
               max: 2
       runner:
@@ -803,7 +803,7 @@
   CinderVolumes.create_nested_snapshots_and_attach_volume:
     -
       args:
-          volume_size:
+          size:
               min: 1
               max: 2
           nested_level:

tests/unit/fakes.py

@@ -1288,6 +1288,7 @@ class FakeRunner(object):
 
 
 class FakeScenario(base.Scenario):
+    """Fake Scenario class."""
 
     def idle_time(self):
         return 0