Correct indication of complete key from "partial"

Reserve_ids indicates complete_key in its typespec and in its type-checking, but says "Partial" in the description after the typespec. I also believe "use as a base for reserved IDs" is ambiguous, but I'm not familiar enough with the underlying API to know a better description since I'm not 100% sure on the behavior is supposed to be.

google/cloud/datastore/client.py

@@ -667,7 +667,7 @@ def reserve_ids(self, complete_key, num_ids):
         """Reserve a list of IDs from a complete key.
 
         :type complete_key: :class:`google.cloud.datastore.key.Key`
-        :param complete_key: Partial key to use as base for reserved IDs.
+        :param complete_key: Complete key to use as base for reserved IDs.
 
         :type num_ids: int
         :param num_ids: The number of IDs to reserve.