Use consistent naming for enforce_scope option

Tempest and a few other plugins such as manila-tempest-plugin registers
the option to enable scope enforcement tests in the [enforce_scope]
option. This renames the option so that this plugin follows that
standard.

Change-Id: Ibd6962947c64f04ff1948a19c4afe9f26d0b47bb
diff --git a/.zuul.yaml b/.zuul.yaml
index 2f38e5d..4906ab0 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -165,8 +165,8 @@
             #  global_default: true
         test-config:
           $TEMPEST_CONFIG:
-            barbican_rbac_scope_verification:
-              enforce_scope: True
+            enforce_scope:
+              barbican: True
             # barbican_tempest:
             #  enable_multiple_secret_stores: True