Fix all-nodes.sh for python3
Fix all-nodes.sh for python3

The unicode function no longer exists in python3 so let's just designate
the string as unicode since we're doing replacement in bash anyway.

Change-Id: I3226a3a16eec711097c30929946cb2d36646c4cc
Related-Blueprint: python3-support

openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,openstack/tripleo-heat-templates,dprince/tripleo-heat-templates