Rename notification/task to notification/tasks

We're using zaqar.notification.tasks to look for the notifier
driver by stevedore, so this patch just rename the package
name to keep consistence. No impact for end user and migration.

Change-Id: I7694af4dbc4f73703e429560fb0a1457f3e1193a

doc/source/api/zaqar.notification.tasks.mailto.rst

@@ -0,0 +1,7 @@
+The :mod:`zaqar.notification.tasks.mailto` module
+==================================================
+
+.. automodule:: zaqar.notification.tasks.mailto
+  :members:
+  :undoc-members:
+  :show-inheritance:

doc/source/api/zaqar.notification.tasks.webhook.rst

@@ -1,7 +1,7 @@
-The :mod:`zaqar.notification.task.webhook` module
+The :mod:`zaqar.notification.tasks.webhook` module
 ==================================================
 
-.. automodule:: zaqar.notification.task.webhook
+.. automodule:: zaqar.notification.tasks.webhook
   :members:
   :undoc-members:
   :show-inheritance:

setup.cfg

@@ -69,9 +69,9 @@ zaqar.storage.redis.driver.queue.stages =
     message_queue_handler = zaqar.storage.redis.messages:MessageQueueHandler
 
 zaqar.notification.tasks =
-    http = zaqar.notification.task.webhook:WebhookTask
-    https = zaqar.notification.task.webhook:WebhookTask
-    mailto = zaqar.notification.task.mailto:MailtoTask
+    http = zaqar.notification.tasks.webhook:WebhookTask
+    https = zaqar.notification.tasks.webhook:WebhookTask
+    mailto = zaqar.notification.tasks.mailto:MailtoTask
 
 tempest.test_plugins =
     zaqar_tests = zaqar.tests.tempest_plugin.plugin:ZaqarTempestPlugin