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

Conflicts:
	neutron/common/utils.py

Change-Id: Ibe3f1b2eb10b9601ad76ec24b7f0e3551b4013e2
(cherry picked from commit 7508170498949818aed02ba0fd9b7f861e596320)
Merge "Common decorator for caching methods" into stable/icehouse