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: I9e883798129ee3ea692e63cf0466b9cfd400a01d

Juniper/nova,jianghuaw/nova,jianghuaw/nova,rahulunair/nova,vmturbo/nova,alaski/nova,cloudbase/nova,vmturbo/nova,mahak/nova,mahak/nova,gooddata/openstack-nova,rajalokan/nova,hanlind/nova,rahulunair/nova,Juniper/nova,klmitch/nova,hanlind/nova,klmitch/nova,mikalstill/nova,vmturbo/nova,phenoxim/nova,rahulunair/nova,Juniper/nova,Juniper/nova,rajalokan/nova,gooddata/openstack-nova,openstack/nova,sebrandon1/nova,sebrandon1/nova,openstack/nova,gooddata/openstack-nova,klmitch/nova,vmturbo/nova,mahak/nova,alaski/nova,gooddata/openstack-nova,rajalokan/nova,cloudbase/nova,sebrandon1/nova,openstack/nova,hanlind/nova,klmitch/nova,jianghuaw/nova,rajalokan/nova,mikalstill/nova,phenoxim/nova,cloudbase/nova,jianghuaw/nova,mikalstill/nova