add ssh keepalive to perl ssh connection

scripts/Mars.pm

@@ -35,6 +35,7 @@ sub ssh_connect {
             master_opts => [
                 -o => 'BatchMode=yes',
                 -o => 'StrictHostKeyChecking=accept-new',
+                -o => 'ServerAliveInterval=60',
             ],
         );
         $_remote->error and die 'SSH connection failed: ' . $_remote->error;