Introduce a new configuration option - windows_metadata_route.
Specifies whether an explicit route for metadata proxy access
on windows should be added.
The default value will be True for backward compatibility.
This option will need to be set to False for some guest OSes such
as RHEL8 as a duplicate metadata route can cause failures while
setting up networking.
Change-Id: If7507d0d4242cce2c73c7a2239149ec35fef232f