Fix key expiry when using sadd

We are passing prepared_name (namespace appended) to BU cache's expire
method which again appends the namespace. Due to this, the following
commands get executed:

SADD "CB-prod:Review:ws_cache_de0eedbf-e2d9-3a64-8e3e-51d68994cee3" "\xd9\x92list_entity_id=de0eedbf-e2d9-3a64-8e3e-51d68994cee3_user_id=None_sort=published_on_sort_order=None_limit=1_offset=0_language=None_review_type=None"
PEXPIRE "CB-prod:Review:CB-prod:Review:ws_cache_de0eedbf-e2d9-3a64-8e3e-51d68994cee3" "1800000"

As we can see, the pexpired key is wrong. Therefore, the sadd'ed keys
live with infinite TTL in redis. Fix this by passing the un-prepared
name to expire method.

brainzutils/cache.py

@@ -337,7 +337,7 @@ def sadd(name, keys, expirein, encode=True, namespace=None):
         keys = {_encode_val(key) for key in keys}
 
     result = _r.sadd(prepared_name, *keys)
-    expire(prepared_name, expirein, namespace)
+    expire(name, expirein, namespace)
     return result