We need to use a workaround for VPN connection state. There is a bug somewhere
causing that vpn-state-changed signal is not issued on active VPN connection.
Debugging showed that D-Bus PropertiesChanged and VpnStateChanged signals are
not processed properly. That's why libnm-glib's VPN connection object is not
updated. The issue may lie in libnm-glib or even in dbus-glib.
I wasn't able to get VpnStateChanged signal via dbus-glib
(dbus_g_proxy_add_signal() and dbus_g_proxy_connect_signal()), however received
the signal successfully using GDBus.

Until the issue is analyzed and fixed, we need to ask for VPN state of active
VPN connection every second in order to show progress and exit correctly.