L3 schedulers support

Icehouse brings new schedulers for virtual routing.
This patch aims to:
- add router_scheduler_driver flag support
- document which schedulers we could use

Change-Id: I9ed4464201e1b888ae7474221babe8e5aad38642
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge "L3 schedulers support"
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

Change-Id: I0e892c4183bd2bf1910b9b6758c1759475053529
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>