Fix 'spacing' parameters for periodic tasks

conductor.manager module contains 'spacing' parameters for periodic
tasks, they do not work because manager module imported before
parsing config options.
There is not such problem in Nova which uses create() method in class
derived from common Service for lazy loading manager module.
Because this derived class not needed for Ironic simple load_manager
function added to common.service.

Partial-Bug: #1279774
Change-Id: Ib31024c8eaf75d38de09983459d86125847cdf30

ironic/cmd/conductor.py

@@ -26,7 +26,6 @@ from oslo.config import cfg
 from ironic.openstack.common import service
 
 from ironic.common import service as ironic_service
-from ironic.conductor import manager
 
 CONF = cfg.CONF
 
@@ -35,6 +34,8 @@ def main():
     # Pase config file and command line options, then start logging
     ironic_service.prepare_service(sys.argv)
 
-    mgr = manager.ConductorManager(CONF.host, manager.MANAGER_TOPIC)
+    mgr = ironic_service.load_manager('ironic.conductor.manager',
+                                      'ConductorManager',
+                                       CONF.host)
     launcher = service.launch(mgr)
     launcher.wait()

ironic/common/service.py

@@ -21,6 +21,7 @@ import socket
 from oslo.config import cfg
 
 from ironic.openstack.common import context
+from ironic.openstack.common import importutils
 from ironic.openstack.common import log
 from ironic.openstack.common import periodic_task
 from ironic.openstack.common import rpc
@@ -67,3 +68,9 @@ def prepare_service(argv=[]):
                                          ])
     cfg.CONF(argv[1:], project='ironic')
     log.setup('ironic')
+
+
+def load_manager(manager_modulename, manager_classname, host):
+    manager_module = importutils.import_module(manager_modulename)
+    manager_class = getattr(manager_module, manager_classname)
+    return manager_class(host, manager_module.MANAGER_TOPIC)