Use six.wraps

There is a slight difference in functools.wraps on python3.x and
on python2.x in regards to the __wrapped__ attribute that the six
version makes transparent; so instead of using the functools one
just use the six one to gain the added compatability.

Change-Id: Iccf2aede08504469c148ee5f81f448cadfc08d5e
Merge "Use six.wraps"