Feature/filestorage securityservices delete (#133)

* sfs: Add support for security services Delete

* sfs: Add acceptance tests for security service Delete
diff --git a/openstack/sharedfilesystems/v2/securityservices/requests.go b/openstack/sharedfilesystems/v2/securityservices/requests.go
index eca9fe5..1253d33 100644
--- a/openstack/sharedfilesystems/v2/securityservices/requests.go
+++ b/openstack/sharedfilesystems/v2/securityservices/requests.go
@@ -59,3 +59,9 @@
 	})
 	return
 }
+
+// Delete will delete the existing SecurityService with the provided ID.
+func Delete(client *gophercloud.ServiceClient, id string) (r DeleteResult) {
+	_, r.Err = client.Delete(deleteURL(client, id), nil)
+	return
+}