Add endpoint_type config option

Prior to their removal from the tempest repository, the heat tests
supported an endpoint_type option[1] to configure which endpoint
interface to use in its requests to the Orchestration service and other
OpenStack services. This patch adds back this support so that users can
configure the heat tests to run against non-public interfaces.

[1] http://git.openstack.org/cgit/openstack/tempest/tree/tempest/config.py?h=17.2.0#n943

Change-Id: Id86f90e428136198b4244f12da5eb53f673fd788
diff --git a/heat_tempest_plugin/config.py b/heat_tempest_plugin/config.py
index 761eddc..6f39abb 100644
--- a/heat_tempest_plugin/config.py
+++ b/heat_tempest_plugin/config.py
@@ -67,6 +67,10 @@
                     "is used"),
     cfg.StrOpt('region',
                help="The region name to use"),
+    cfg.StrOpt('endpoint_type',
+               default='public',
+               choices=['public', 'admin', 'internal'],
+               help="The endpoint type to use for the orchestration service."),
     cfg.StrOpt('instance_type',
                help="Instance type for tests. Needs to be big enough for a "
                     "full OS plus the test workload"),