Convert strutils to oslo.utils.encodeutils

Convert the encode/decode functions from oslo-incubator to use
oslo.utils encodeutils, as the incubator functions are now
deprecated.

Also syncs oslo-incubator to 62394a3 to purge usage of strutils
from the openstack/common modules.

Note includes oslo fix https://review.openstack.org/#/c/133290/
which we need or the python3 tests won't pass.

Change-Id: I630fe3f3ce14ae745a8417bfe6552acd31341c9c
Partial-Bug: #1380629
Merge "Convert strutils to oslo.utils.encodeutils"