remove biglock usage from ipsectunnel.sh

Biglock breaks creating VPN's when other scripts run at the
same time that also use the same biglock. These other scripts
do nothing that could harm our deployment and even multiple
vpn's can safely be created simultaniously.
renamed $leftgw to $leftnexthop to make clear what it does
starting the tunnel will make it keep trying until it connects

Changed 'auto=add' to 'auto=start' to make sure the tunnel starts.
When both sides are there they will connect. This resolves the
issue that there is only a small time frame in which the VPN
would connect.
add a flag -c whether or not to check the VPN on create

Changed default to no, as the other side may not be up yet.
If this check fails, the VPN enters Error state and will not
work. It's safe to just let it connect on its own so it will
connect when it can.
prevent CloudStack from removing the VPN connection

If connecting the VPN takes some time, for example because
the other end is not (yet) up, CloudStack will delete
the VPN because the ipsectunnel.sh does not return in time.
The VPN connection then enters the Error state.

This change makes sure ipsectunnel.sh returns in time,
and lets ipsec connect in the background. If it all fails,
the connection enters Disconnected.
made iptables for the VPN connection more secure

Added destination and source definition. Flag -S can be used
to ignore this. It's the new default as it is more secure
and does not impact the way things work (backwords compatible).