Bug #1121119
Allows the NVP plugin to leverage the metadata proxy, by creating an
ad-hoc topology for allowing access to a metadata proxy from a NVP
router leveraging existing agents.
This patch also removes previous code for metadata support in the
NVP plugin, which was based on DHCP Option 121. This is now provided
by the dhcp agent as well.
Change-Id: If37ef388e063f40bb06908ee2f72c431f29dac31