Replace basestring with six.string_types
Replace basestring with six.string_types

Partial implement: blueprint py33-support

Change-Id: Ibf1c63d407698f37b333da8f90bbdedbd9512c75

openstack/python-ironicclient,varunarya10/python-ironicclient,NaohiroTamura/python-ironicclient,bcrochet/python-ironicclient,ramineni/myclient,CiscoUcs/UCS-python-ironicclinet,JioCloud/python-ironicclient,redhat-openstack/python-ironicclient,openstack/python-ironicclient,NaohiroTamura/python-ironicclient,rdo-management/python-ironicclient,citrix-openstack-build/python-ironicclient