Add strategy template doc

Developer should provide a detailled documentation about his strategy
algorithm to make it even easier to use by a Watcher end user.
I propose in this changeset a template for strategy documentation.
you will find also a example with basic consolidation strategy.

Change-Id: I66da1a33b87a94b508dd23ac7dce4cae6f4e068b

watcher/decision_engine/goal/efficacy/specs.py

@@ -37,9 +37,9 @@ class ServerConsolidation(base.EfficacySpecification):
             indicators.InstanceMigrationsCount(),
         ]
 
-    def get_global_efficacy_indicator(self, indicators_map):
+    def get_global_efficacy_indicator(self, indicators_map=None):
         value = 0
-        if indicators_map.instance_migrations_count > 0:
+        if indicators_map and indicators_map.instance_migrations_count > 0:
             value = (float(indicators_map.released_compute_nodes_count) /
                      float(indicators_map.instance_migrations_count)) * 100
 

watcher/decision_engine/model/collector/nova.py

@@ -28,16 +28,10 @@ LOG = log.getLogger(__name__)
 
 
 class NovaClusterDataModelCollector(base.BaseClusterDataModelCollector):
-    """nova
+    """Nova cluster data model collector
 
-    *Description*
-
-    This Nova cluster data model collector creates an in-memory representation
-    of the resources exposed by the compute service.
-
-    *Spec URL*
-
-    <None>
+       The Nova cluster data model collector creates an in-memory
+       representation of the resources exposed by the compute service.
     """
 
     def __init__(self, config, osc=None):

watcher/decision_engine/strategy/strategies/basic_consolidation.py

@@ -25,6 +25,14 @@ it becomes necessary to migrate VMs among servers to lower the costs. However,
 migration of VMs introduces runtime overheads and consumes extra energy, thus
 a good server consolidation strategy should carefully plan for migration in
 order to both minimize energy consumption and comply to the various SLAs.
+
+This algorithm not only minimizes the overall number of used servers, but also
+minimizes the number of migrations.
+
+It has been developed only for tests. You must have at least 2 physical compute
+nodes to run it, so you can easilly run it on DevStack. It assumes that live
+migration is possible on your OpenStack cluster.
+
 """
 
 from oslo_log import log
@@ -39,28 +47,7 @@ LOG = log.getLogger(__name__)
 
 
 class BasicConsolidation(base.ServerConsolidationBaseStrategy):
-    """Basic offline consolidation using live migration
-
-    *Description*
-
-    This is server consolidation algorithm which not only minimizes the overall
-    number of used servers, but also minimizes the number of migrations.
-
-    *Requirements*
-
-    * You must have at least 2 physical compute nodes to run this strategy.
-
-    *Limitations*
-
-    - It has been developed only for tests.
-    - It assumes that the virtual machine and the compute node are on the same
-      private network.
-    - It assumes that live migrations are possible.
-
-    *Spec URL*
-
-    <None>
-    """
+    """Basic offline consolidation using live migration"""
 
     HOST_CPU_USAGE_METRIC_NAME = 'compute.node.cpu.percent'
     INSTANCE_CPU_USAGE_METRIC_NAME = 'cpu_util'