Plugin multi_tcp_ping: gracefully handle DNS resolution problems

Previously the plugin exited with an error, if the target name could not
be resolved.  Now this problem is handled just like an "unreachable"
situation.

Thanks, nitram2342!

Closes: #1091

plugins/ping/multi_tcp_ping

@@ -108,7 +108,9 @@ sub ping_host {
     $p->service_check(1);
     $p->{port_num} = $host->[1] || $defaults{port};
 
-    ($ret, $time, $ip) = $p->ping($host->[0]);
+    eval {
+        ($ret, $time, $ip) = $p->ping($host->[0]);
+    };
 
     $time = $defaults{unreachable} if !$ret;
     print "${addr}.value $time\n";