Isolated network support

This patch aims to enable support for both:
- isolated metadata which enable metadata support on isolated networks.
- metadata networks which allows for serving metadata requests coming
  from a dedicated metadata access network

Conflicts:
	manifests/agents/dhcp.pp
	spec/classes/neutron_agents_dhcp_spec.rb

Change-Id: I0e892c4183bd2bf1910b9b6758c1759475053529
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
(cherry picked from commit 8654569fb4c53f8648578f8485fad80e3fe69e52)
Merge "Isolated network support" into stable/havana