Allocate public IP address to glance-server nodes

The glance server needs to be accessible from the external network, so
that OpenStack command line tools work.

We only do this if binding to all addresses.
Stop trying to set bind host in apply_role_pre_chef_call

This was broken as this was setting the wrong attributes, and this is
already done in the common recipe.
Merge pull request #106 from vuntz/allocate-public-ip

Allocate public IP address to glance-server nodes