Enable the quantum metadata agent and disable nova-network

This change allows instances to access the nova metadata service via
the quantum metadata namespace and agent proxies. Now instances can do
'wget http://169.254.169.254/'

It also disables nova-network as it should not be used with quantum and it
adds a lot of unwanted iptables rules.
Merge pull request #4 from djoreilly/metadata

Enable the quantum metadata agent and disable nova-network