add deps for barbican-tempest-plugin

oslo_config and oslo_log are imported in
codes, such as:
https://github.com/openstack/barbican-tempest-plugin
/blob/master/barbican_tempest_plugin/config.py#L16
https://github.com/openstack/barbican-tempest-plugin
/blob/master/barbican_tempest_plugin/tests/scenario/barbican_manager.py#L29
So, we should add them as deps.

Change-Id: Id22657b0169d302bbf62747ef7708d456107c529
diff --git a/requirements.txt b/requirements.txt
index 1afcc6f..bb8df5e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -6,3 +6,5 @@
 
 tempest>=12.1.0  # Apache-2.0
 cryptography!=1.3.0,>=1.0 # BSD/Apache-2.0
+
+oslo.config>=3.22.0 # Apache-2.0