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

doc/source/strategies/basic-server-consolidation.rst

@@ -0,0 +1,96 @@
+==================================
+Basic Offline Server Consolidation
+==================================
+
+Synopsis
+--------
+
+**display name**: ``basic``
+
+**goal**: ``server_consolidation``
+
+    .. watcher-term:: watcher.decision_engine.strategy.strategies.basic_consolidation
+
+Requirements
+------------
+
+Metrics
+*******
+
+The *basic* strategy requires the following metrics:
+
+============================ ============ ======= =======
+metric                       service name plugins comment
+============================ ============ ======= =======
+``compute.node.cpu.percent`` ceilometer_  none
+``cpu_util``                 ceilometer_  none
+============================ ============ ======= =======
+
+.. _ceilometer: http://docs.openstack.org/admin-guide/telemetry-measurements.html#openstack-compute
+
+Cluster data model
+******************
+
+Default Watcher's Compute cluster data model:
+
+    .. watcher-term:: watcher.decision_engine.model.collector.nova.NovaClusterDataModelCollector
+
+Actions
+*******
+
+Default Watcher's actions:
+
+
+    .. list-table::
+       :widths: 30 30
+       :header-rows: 1
+
+       * - action
+         - description
+       * - ``migration``
+         - .. watcher-term:: watcher.applier.actions.migration.Migrate
+       * - ``change_nova_service_state``
+         - .. watcher-term:: watcher.applier.actions.change_nova_service_state.ChangeNovaServiceState
+
+Planner
+*******
+
+Default Watcher's planner:
+
+    .. watcher-term:: watcher.decision_engine.planner.default.DefaultPlanner
+
+Configuration
+-------------
+
+Strategy parameter is:
+
+====================== ====== ============= ===================================
+parameter              type   default Value description
+====================== ====== ============= ===================================
+``migration_attempts`` Number 0             Maximum number of combinations to
+                                            be tried by the strategy while
+                                            searching for potential candidates.
+                                            To remove the limit, set it to 0
+====================== ====== ============= ===================================
+
+Efficacy Indicator
+------------------
+
+.. watcher-func::
+  :format: literal_block
+
+  watcher.decision_engine.goal.efficacy.specs.ServerConsolidation.get_global_efficacy_indicator
+
+How to use it ?
+---------------
+
+.. code-block:: shell
+
+    $ openstack optimize audittemplate create \
+      at1 server_consolidation --strategy basic
+
+    $ openstack optimize audit create -a at1 -p migration_attempts=4
+
+External Links
+--------------
+None.

doc/source/strategies/strategies.rst

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+Strategies
+==========
+
+.. toctree::
+   :glob:
+   :maxdepth: 1
+
+   ./*

doc/source/strategies/strategy-template.rst

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+=============
+Strategy name
+=============
+
+Synopsis
+--------
+
+**display name**:
+
+**goal**:
+
+Add here a complete description of your strategy
+
+Requirements
+------------
+
+Metrics
+*******
+
+Write here the list of metrics required by your strategy algorithm (in the form
+ of a table). If these metrics requires specific Telemetry plugin or other
+ additional software, please explain here how to deploy them (and add link to
+ dedicated installation guide).
+
+Example:
+
+======================= ============ ======= =======
+metric                  service name plugins comment
+======================= ============ ======= =======
+compute.node.*          ceilometer_  none    one point every 60s
+vm.cpu.utilization_perc monasca_     none
+power                   ceilometer_  kwapi_  one point every 60s
+======================= ============ ======= =======
+
+
+.. _ceilometer: http://docs.openstack.org/admin-guide/telemetry-measurements.html#openstack-compute
+.. _monasca: https://github.com/openstack/monasca-agent/blob/master/docs/Libvirt.md
+.. _kwapi: https://kwapi.readthedocs.io/en/latest/index.html
+
+
+Cluster data model
+******************
+
+Default Watcher's cluster data model.
+
+or
+
+If your strategy implementation requires a new cluster data model, please
+ describe it in this section, with a link to model plugin's installation guide.
+
+Actions
+*******
+
+Default Watcher's actions.
+
+or
+
+If your strategy implementation requires new actions, add the list of Action
+ plugins here (in the form of a table) with a link to the plugin's installation
+ procedure.
+
+======== =================
+action   description
+======== =================
+action1_ This action1 ...
+action2_ This action2 ...
+======== =================
+
+.. _action1 : https://github.com/myrepo/watcher/plugins/action1
+.. _action2 : https://github.com/myrepo/watcher/plugins/action2
+
+Planner
+*******
+
+Default Watcher's planner.
+
+or
+
+If your strategy requires also a new planner to schedule built actions in time,
+ please describe it in this section, with a link to planner plugin's
+ installation guide.
+
+Configuration
+-------------
+
+If your strategy use configurable parameters, explain here how to tune them.
+
+
+Efficacy Indicator
+------------------
+
+Add here the Efficacy indicator computed by your strategy.
+
+How to use it ?
+---------------
+
+.. code-block:: shell
+
+    $ Write the command line to create an audit with your strategy.
+
+External Links
+--------------
+
+If you have written papers, blog articles .... about your strategy into Watcher,
+ or if your strategy is based from external publication(s), please add HTTP
+ links and references in this section.
+
+- `link1 <http://www.link1.papers.com>`_
+- `link2 <http://www.link2.papers.com>`_