Fix support for proxy URL from tempest.conf

Fix support for using HTTP proxy server to connect to
OpenStack REST API services.

Closes-Bug: #1764375
Change-Id: Ic1f3ab388be2ec3ccb82102cbb2abad157817d54
diff --git a/neutron_tempest_plugin/api/clients.py b/neutron_tempest_plugin/api/clients.py
index 875992e..14f6714 100644
--- a/neutron_tempest_plugin/api/clients.py
+++ b/neutron_tempest_plugin/api/clients.py
@@ -35,7 +35,8 @@
         'disable_ssl_certificate_validation':
             CONF.identity.disable_ssl_certificate_validation,
         'ca_certs': CONF.identity.ca_certificates_file,
-        'trace_requests': CONF.debug.trace_requests
+        'trace_requests': CONF.debug.trace_requests,
+        'proxy_url': CONF.service_clients.proxy_url
     }
 
     # NOTE: Tempest uses timeout values of compute API if project specific