Set a default region for clients

Clients initialized for tests.api.* tests do not have defined values
for region [1]. Because of that the clients connect to the first
available service endpoint that they find (see this line in
tempest [2]). This can cause issues when there are multiple endpoints
on a system for barbican (admin, internal, public).

This change sets a default value for key_manager.region config option
to 'regionOne' and ensures that clients defined on the side of
barbican-tempest-plugin are intialised with this value.

[1] https://opendev.org/openstack/barbican-tempest-plugin/src/branch/master/barbican_tempest_plugin/tests/api/base.py#L91
[2] https://opendev.org/openstack/tempest/src/branch/master/tempest/lib/auth.py#L586

Change-Id: Ic9ae00c663cca6b83dc961b984cf129d1c33afc4
diff --git a/barbican_tempest_plugin/config.py b/barbican_tempest_plugin/config.py
index da78d15..446a327 100644
--- a/barbican_tempest_plugin/config.py
+++ b/barbican_tempest_plugin/config.py
@@ -43,7 +43,12 @@
                     "min_microversion and max_microversion. "
                     "If both values are not specified, Tempest avoids tests "
                     "which require a microversion. Valid values are string "
-                    "with format 'X.Y' or string 'latest'")
+                    "with format 'X.Y' or string 'latest'"),
+    cfg.StrOpt('region',
+               default='regionOne',
+               help="The barbican region name to use. If no such region is"
+                    "found in the service catalog, the first found one is "
+                    "used.")
 ]
 
 barbican_tempest_group = cfg.OptGroup(