OSP Tempest fails when using Ceph RadosGW as swift endpoint

Issue

Tempest fails with error 404 when Ceph RadosGW is used as Swift endpoint:

tools/config_tempest.py --debug --create identity.uri $OS_AUTH_URL identity.admin_username $OS_USERNAME identity.admin_password $OS_PASSWORD identity.admin_tenant_name $OS_TENANT_NAME object-storage.operator_role SwiftOperator
[...]
2017-01-10 15:54:21.786 19457 CRITICAL tempest [-] ServiceError: Request on service 'object-store' with url 'https://my.rgw.hostname/info' failed with code 404
2017-01-10 15:54:21.786 19457 TRACE tempest Traceback (most recent call last):
2017-01-10 15:54:21.786 19457 TRACE tempest   File "tools/config_tempest.py", line 742, in <module>
2017-01-10 15:54:21.786 19457 TRACE tempest     main()
2017-01-10 15:54:21.786 19457 TRACE tempest   File "tools/config_tempest.py", line 144, in main
2017-01-10 15:54:21.786 19457 TRACE tempest     object_store_discovery=conf.get_bool_value(swift_discover))
2017-01-10 15:54:21.786 19457 TRACE tempest   File "/root/tempest/tempest/common/api_discovery.py", line 157, in discover
2017-01-10 15:54:21.786 19457 TRACE tempest     services[name]['extensions'] = service.get_extensions()
2017-01-10 15:54:21.786 19457 TRACE tempest   File "/root/tempest/tempest/common/api_discovery.py", line 111, in get_extensions
2017-01-10 15:54:21.786 19457 TRACE tempest     top_level_path="info")
2017-01-10 15:54:21.786 19457 TRACE tempest   File "/root/tempest/tempest/common/api_discovery.py", line 53, in do_get
2017-01-10 15:54:21.786 19457 TRACE tempest     " with code %d" % (self.name, url, r.status))
2017-01-10 15:54:21.786 19457 TRACE tempest ServiceError: Request on service 'object-store' with url 'https://my.rgw.hostname:8081/info' failed with code 404
2017-01-10 15:54:21.786 19457 TRACE tempest