Use openstacksdk submit_task

Task manager stats sending was broken with openstacksdk updates and
fixed in I8617ab2895d1544a6902ae5a3d6a97b87bfd2ec9.

What used to happen is that openstacksdk run_task() would call
post_run_task(); however with changes to use a threadpool this became
an async call so was not reflecting the post-run state but just the
post-insert-into-threadpool-queue state.

The referenced change moved the post_run_task() call into
submit_task(), where it is called after the task has been wait()ed
for (and actually run).

Unfortunatley, since this file overrides submit_task, it means that
post_run_task is not being called any more and we are not producing
timing stats.

I believe we can use the openstacksdk task manager's submit_task
directly.  There are two differences; the "raw" argument was removed
from upstream with I7b46e263a76d84573bdfbbece57b1048764ed939 and is no
longer necessary.  The ManagerStoppedException is private to this file
and doesn't appear to have an external dependencies; thus the
openstacksdk's TaskManagerStopped exception will work just the same.

Change-Id: I427e6ae9e4beae6d551427fc12a3cde2c1d03aba

nodepool/task_manager.py

@@ -39,10 +39,6 @@ def _transform_task_name(task_name):
     )
 
 
-class ManagerStoppedException(Exception):
-    pass
-
-
 class TaskManager(openstack_task_manager.TaskManager):
     log = logging.getLogger("nodepool.TaskManager")
 
@@ -101,10 +97,3 @@ class TaskManager(openstack_task_manager.TaskManager):
             key = 'nodepool.task.%s.%s' % (self.name, task_name)
             self.statsd.timing(key, int(elapsed_time * 1000))
             self.statsd.incr(key)
-
-    def submit_task(self, task, raw=False):
-        if not self._running:
-            raise ManagerStoppedException(
-                "Manager %s is no longer running" % self.name)
-        self.queue.put(task)
-        return task.wait()

releasenotes/notes/openstacksdk-stats-fix-f0f8da97cfd52328.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - Fixes a regression of missing task statistics with OpenstackSDK
+    versions greater than 0.19.0.