Updated openstack/openstack
Project: openstack/nova  8af5c61ab0d26bcc8d487ce664cd36d7b6a17f65
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Nova-all: Replace basestring by six for python3 compatability

The builtin basestring abstract type was removed in python3,
use str instead, we need to using six.string_types to replace
the basestring for py3 compatibility.

Partial Implements bp: basestring-py3-compatible

Change-Id: I17e87e49e7ebf3cc9c391e9beace8c45d2d2b689