Command line option to show VRRP status

This commit adds a new command line option, -s, --vrrp-status, which will show the status of VRRP instances.

Example output:
<pre>
  VRRP Instance             : VI_1
     Interface              : eth0
     Virtual Router ID      : 1
     State                  : BACKUP
     Virtual IP address     : 192.168.2.99
     Advertisement interval : 1.00 sec
     Preemption             : Disabled
     Multicast group        : 192.168.2.2
     Priority               : 100
     Effective Priority     : 100
     Master router          : 192.168.2.1 priority 150
     Master down interval   : 3.0
</pre>