Common decorator for caching methods

Decorator caches methods' results, the key is composed from function
name and its parameters. Implementation of cache itself should be in
object implementing decorated method. Cache backend should be taken
from oslo-incubator.

Related-Bug: #1276440
Change-Id: Ibe3f1b2eb10b9601ad76ec24b7f0e3551b4013e2
Merge "Common decorator for caching methods"