Replace unicode with six.text_type
Replace unicode with six.text_type

The Unicode type is 'unicode' in Python 2 and 'str' on Python 3.
This patch replaces unicode with six.text_type to make Nova
compatible with Python 2 and Python 3.

Blueprint nova-python3
Change-Id: Ib9e64b2b63d1e4f343dc2d27f409436305143675

rajalokan/nova,hanlind/nova,openstack/nova,rajalokan/nova,phenoxim/nova,hanlind/nova,bigswitch/nova,CEG-FYP-OpenStack/scheduler,bigswitch/nova,klmitch/nova,sebrandon1/nova,cernops/nova,cyx1231st/nova,vmturbo/nova,jianghuaw/nova,hanlind/nova,mahak/nova,zhimin711/nova,cloudbase/nova,jianghuaw/nova,sebrandon1/nova,klmitch/nova,alaski/nova,rahulunair/nova,sebrandon1/nova,openstack/nova,klmitch/nova,mikalstill/nova,alaski/nova,dims/nova,rahulunair/nova,mahak/nova,BeyondTheClouds/nova,gooddata/openstack-nova,Juniper/nova,rajalokan/nova,cernops/nova,jianghuaw/nova,vmturbo/nova,rahulunair/nova,mikalstill/nova,vmturbo/nova,Juniper/nova,gooddata/openstack-nova,gooddata/openstack-nova,CEG-FYP-OpenStack/scheduler,BeyondTheClouds/nova,gooddata/openstack-nova,NeCTAR-RC/nova,rajalokan/nova,cloudbase/nova,jianghuaw/nova,cyx1231st/nova,cloudbase/nova,openstack/nova,BeyondTheClouds/nova,vmturbo/nova,dims/nova,phenoxim/nova,mikalstill/nova,zhimin711/nova,mahak/nova,Juniper/nova,cernops/nova,NeCTAR-RC/nova,klmitch/nova,Juniper/nova