vyatta-openvpn: correct wrong node name usage for persistent tunnels

Correction for wrong node name usage in the code for persistent openvpn
tunnels, added for Bug #7 and Bug #313

Bug #7 http://bugzilla.vyos.net/show_bug.cgi?id=7
Bug #313 http://bugzilla.vyos.net/show_bug.cgi?id=313
vyatta-openvpn: persistent tunnels in server mode and allow full reset

Allow OpenVPN tunnels (vtun) that are configured for server mode
operation to be set as persistent (TUN/TAP interfaces aren't closed
and reopened on a reset).  Check if the tunnel is configured for
persistence when 'reset openvpn interface' is run from the CLI, if it
then prompt the user if an interface reset is required along with the
tunnel reset (defaults to yes).

Bug #7 http://bugzilla.vyos.net/show_bug.cgi?id=7
Bug #313 http://bugzilla.vyos.net/show_bug.cgi?id=313