Fix NVP plugin not notifying metadata access network to DHCP agent

Bug 1133395

Due to recent changes in notification logic between Quantum and the DHCP
agent, the notifier the NVP plugin previously used for metadata access
network was not working anymore and needed to be replaced

Change-Id: Ifa0ea55116cf5ef6d546d28ca52e643987b3e5a0
Merge "Fix NVP plugin not notifying metadata access network to DHCP agent"