Make the admin role configurable within tempest

Adds a configuration variable for the admin role.

Change-Id: Ib7f1eaaefedebd6f0d608b0645950d0b64d87f7a
Closes-Bug: #1224742
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 8d96858..3a33fd6 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -53,6 +53,9 @@
 # The above administrative user's tenant name
 admin_tenant_name = admin
 
+# The role that is required to administrate keystone.
+admin_role = admin
+
 [compute]
 # This section contains configuration options used when executing tests
 # against the OpenStack Compute API.