Cluster data model collector plugin documentation

In this changeset, I wrote down the documentation on how to implement
a cluster data model collector plugin for Watcher.

This documentation corresponds to part 1 of the associated
specification.

Change-Id: Iac72b933df95252163033cd559d13348075a9b16
Partially-Implements: blueprint cluster-model-objects-wrapper

watcher/decision_engine/goal/goals.py

@@ -72,7 +72,7 @@ class Unclassified(base.Goal):
 
 
 class ServerConsolidation(base.Goal):
-    """ServerConsolidation
+    """Server Consolidation
 
     This goal is for efficient usage of compute server resources in order to
     reduce the total number of servers.
@@ -97,7 +97,7 @@ class ServerConsolidation(base.Goal):
 
 
 class ThermalOptimization(base.Goal):
-    """ThermalOptimization
+    """Thermal Optimization
 
     This goal is used to balance the temperature across different servers.
     """
@@ -121,7 +121,7 @@ class ThermalOptimization(base.Goal):
 
 
 class WorkloadBalancing(base.Goal):
-    """WorkloadBalancing
+    """Workload Balancing
 
     This goal is used to evenly distribute workloads across different servers.
     """
@@ -145,6 +145,10 @@ class WorkloadBalancing(base.Goal):
 
 
 class AirflowOptimization(base.Goal):
+    """Workload Balancing
+
+    This goal is used to optimize the air flow within a cloud infrastructure.
+    """
 
     @classmethod
     def get_name(cls):

watcher/decision_engine/model/mapping.py

@@ -30,7 +30,7 @@ class Mapping(object):
         self.lock = threading.Lock()
 
     def map(self, hypervisor, vm):
-        """Select the hypervisor where the instance are launched
+        """Select the hypervisor where the instance is launched
 
         :param hypervisor: the hypervisor
         :param vm: the virtual machine or instance