caches: fixed unicode mismatch with types

vcsserver/lib/rc_cache/backends.py

@@ -265,7 +265,7 b' class BaseRedisBackend(redis_backend.Red'
 
     def get_mutex(self, key):
         if self.distributed_lock:
-            lock_key = redis_backend.u(u'_lock_{0}'.format(safe_unicode(key)))
+            lock_key = u'_lock_{0}'.format(safe_unicode(key))
             return get_mutex_lock(self.client, lock_key, self._lock_timeout,
                                   auto_renewal=self._lock_auto_renewal)
         else: