nova-compute fails to start even if [placement]/region_name is set

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, as seen here:

http://logs.openstack.org/77/554577/1/check/tempest-full-py3/df52956/controller/logs/screen-n-cpu.txt.gz#_Mar_20_15_16_30_122538

Mar 20 15:16:30.122538 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: ERROR oslo_service.service [None req-19eb4465-6304-40fe-bb23-4bc7ce96f03a None None] Error starting thread.: nova.exception.PlacementNotConfigured: This compute is not configured to talk to the placement service. Configure the [placement] section of nova.conf and restart the service.
Mar 20 15:16:30.122790 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: ERROR oslo_service.service Traceback (most recent call last):
Mar 20 15:16:30.122925 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: ERROR oslo_service.service File "/usr/local/lib/python3.5/dist-packages/oslo_service/service.py", line 729, in run_service
Mar 20 15:16:30.123087 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: ERROR oslo_service.service service.start()
Mar 20 15:16:30.123219 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: ERROR oslo_service.service File "/opt/stack/nova/nova/service.py", line 162, in start
Mar 20 15:16:30.123348 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: ERROR oslo_service.service self.manager.init_host()
Mar 20 15:16:30.123484 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: ERROR oslo_service.service File "/opt/stack/nova/nova/compute/manager.py", line 1135, in init_host
Mar 20 15:16:30.123628 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: ERROR oslo_service.service raise exception.PlacementNotConfigured()
Mar 20 15:16:30.123749 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: ERROR oslo_service.service nova.exception.PlacementNotConfigured: This compute is not configured to talk to the placement service. Configure the [placement] section of nova.conf and restart the service.
Mar 20 15:16:30.123870 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: ERROR oslo_service.service

From the config:

Mar 20 15:16:30.044109 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: DEBUG oslo_service.service [None req-19eb4465-6304-40fe-bb23-4bc7ce96f03a None None] placement.os_region_name = None {{(pid=19979) log_opt_values /usr/local/lib/python3.5/dist-packages/oslo_config/cfg.py:2898}}
Mar 20 15:16:30.044351 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: DEBUG oslo_service.service [None req-19eb4465-6304-40fe-bb23-4bc7ce96f03a None None] placement.randomize_allocation_candidates = False {{(pid=19979) log_opt_values /usr/local/lib/python3.5/dist-packages/oslo_config/cfg.py:2898}}
Mar 20 15:16:30.044612 ubuntu-xenial-ovh-gra1-0003080089 nova-compute[19979]: DEBUG oslo_service.service [None req-19eb4465-6304-40fe-bb23-4bc7ce96f03a None None] placement.region_name = RegionOne {{(pid=19979) log_opt_values /usr/local/lib/python3.5/dist-packages/oslo_config/cfg.py:2898}}

And this is the code that fails:

https://github.com/openstack/nova/blob/3fd863d8bf2fa1fc09acd08d976689462cffd2e3/nova/compute/manager.py#L1134

That needs to be changed to:

if CONF.placement.os_region_name is None and CONF.placement.region_name is None:
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