Change compute mgr placement check to region_name

Change https://review.openstack.org/#/c/492247/ in queens deprecated the
[placement]/os_region_name config option and you should be using
'region_name' in that group now, and you'll get a deprecation warning if
using 'os_region_name', but if you do that, nova-compute fails to start.

This patch fix the bug by adding [placement]/region_name to the check.

Change-Id: Iea7d5d0d6907adbcb236dc43b5af7469de2ba78b
Closes-Bug: #1757273

nova/compute/manager.py

@@ -1131,7 +1131,7 @@ class ComputeManager(manager.Manager):
         # NOTE(sbauza): We want the compute node to hard fail if it won't be
         # able to provide its resources to the placement API, or it will not
         # be able to be eligible as a destination.
-        if CONF.placement.os_region_name is None:
+        if CONF.placement.region_name is None:
             raise exception.PlacementNotConfigured()
 
         self.driver.init_host(host=self.host)

nova/tests/unit/compute/test_compute_mgr.py

@@ -3711,6 +3711,7 @@ class ComputeManagerUnitTestCase(test.NoDBTestCase):
         # Tests that we fail init_host if the placement section is
         # configured incorrectly.
         self.flags(os_region_name=None, group='placement')
+        self.flags(region_name=None, group='placement')
         self.assertRaises(exception.PlacementNotConfigured,
                           self.compute.init_host)
 

nova/tests/unit/conf_fixture.py

@@ -77,8 +77,7 @@ class ConfFixture(config_fixture.Config):
         self.conf.set_default('keep_alive', False, group="wsgi")
 
         # placement group
-        self.conf.set_default('os_region_name', 'RegionOne',
-                              group='placement')
+        self.conf.set_default('region_name', 'RegionOne', group='placement')
 
         config.parse_args([], default_config_files=[], configure_db=False,
                           init_rpc=False)