Change ping module to use Net::Ping::External

Currently VCL uses the Net::Ping->new("icmp"); module to ping computers.  This module can currently only be run as the root user.

I would suggest that we change the ping module from 

my $p = Net::Ping->new("icmp");
my $result = $p->ping($remote_connection_target, 1);
$p->close();

to

use Net::Ping::External qw(ping);
my $result = ping(host => $remote_connection_target, timeout => 1);

This will help allow vcl to be run as a user other than root.