Add Authentication in VRRP configuration

[sbarguil]

A router will ignore incoming VRRP packets from routers that do not have the same authentication configuration for a VRRP group. VRRP commonly has three authentication schemes:

• No authentication
• Plain text authentication
• MD5 authentication

VRRP packets will be rejected in any of the following cases:

• The authentication schemes differ on the router and in the incoming packet.
• MD5 digests differ on the router and in the incoming packet.
• Text authentication strings differ on the router and in the incoming packet.