Sync strutils from oslo

Sync strutils from oslo which fix safe_encode under py3, this gets
keystone CLI to properly output results.

84d461 Fix a bug in safe_encode where it returns a bytes object in py3

Closes-Bug: 1260824
Change-Id: Idf0f3a51f5cfe3077395b53da66a12955449861f
Revert "Whitelist external netaddr requirement"

This reverts commit 01dc81aa148adaa127281f197047636cf2d2c898.

The netaddr package is now hosted on PyPI, so this workaround is
not needed anymore.

Change-Id: I76957aa5e276036921696f27e18efb5494b33120
Closes-Bug: #1266513
Merge "Sync strutils from oslo"
Merge "Revert "Whitelist external netaddr requirement""