Add ripv2 and ripng - show command

[frederic-loui]

With commit 861b92b it is now possible to have an optimized and common way to query and parse Yang models state xpath.

It is now possible to add show to all other protocols such as ripv2 and ripng

This is the list proposed:

show ripv2 interface
show ripv2 neighbor
show ripv2 route

Respectively:

show ripng interface
show ripng neighbor
show ripng route