RST directive to discover and generate drivers doc

This patchset introduces a new custom directive called 'drivers-doc'
which loads all available drivers under a given namespace and import
their respective docstring into the .rst document.

This patchset also contains some modification/addition to the
docstring of these drivers to make the final document complete.

Change-Id: Ib3df59fa45cea9d11d20fb73a5f0f1d564135bca
Closes-Bug: #1536218
Closes-Bug: #1536735

watcher/applier/actions/change_nova_service_state.py

@@ -27,6 +27,24 @@ from watcher.decision_engine.model import hypervisor_state as hstate
 
 
 class ChangeNovaServiceState(base.BaseAction):
+    """Disables or enables the nova-compute service, deployed on a host
+
+    By using this action, you will be able to update the state of a
+    nova-compute service. A disabled nova-compute service can not be selected
+    by the nova scheduler for future deployment of server.
+
+    The action schema is::
+
+        schema = Schema({
+         'resource_id': str,
+         'state': str,
+        })
+
+    The `resource_id` references a nova-compute service name (list of available
+    nova-compute services is returned by this command: ``nova service-list
+    --binary nova-compute``).
+    The `state` value should either be `ONLINE` or `OFFLINE`.
+    """
 
     STATE = 'state'
 

watcher/applier/actions/migration.py

@@ -31,6 +31,32 @@ LOG = log.getLogger(__name__)
 
 
 class Migrate(base.BaseAction):
+    """Live-Migrates a server to a destination nova-compute host
+
+    This action will allow you to migrate a server to another compute
+    destination host. As of now, only live migration can be performed using
+    this action.
+    .. If either host uses shared storage, you can use ``live``
+    .. as ``migration_type``. If both source and destination hosts provide
+    .. local disks, you can set the block_migration parameter to True (not
+    .. supported for yet).
+
+    The action schema is::
+
+        schema = Schema({
+         'resource_id': str,  # should be a UUID
+         'migration_type': str,  # choices -> "live" only
+         'dst_hypervisor': str,
+         'src_hypervisor': str,
+        })
+
+    The `resource_id` is the UUID of the server to migrate. Only live migration
+    is supported.
+    The `src_hypervisor` and `dst_hypervisor` parameters are respectively the
+    source and the destination compute hostname (list of available compute
+    hosts is returned by this command: ``nova service-list --binary
+    nova-compute``).
+    """
 
     # input parameters constants
     MIGRATION_TYPE = 'migration_type'

watcher/applier/actions/nop.py

@@ -28,6 +28,16 @@ LOG = log.getLogger(__name__)
 
 
 class Nop(base.BaseAction):
+    """logs a message
+
+    The action schema is::
+
+        schema = Schema({
+         'message': str,
+        })
+
+    The `message` is the actual message that will be logged.
+    """
 
     MESSAGE = 'message'
 

watcher/applier/actions/sleep.py

@@ -28,6 +28,16 @@ LOG = log.getLogger(__name__)
 
 
 class Sleep(base.BaseAction):
+    """Makes the executor of the action plan wait for a given duration
+
+    The action schema is::
+
+        schema = Schema({
+         'duration': float,
+        })
+
+    The `duration` is expressed in seconds.
+    """
 
     DURATION = 'duration'