Bad INSTANCE_IP if container has more than one IP

[underdogest]

In entrypoint.sh the line
INSTANCE_IP=$(hostname -I | sed "s= ==g")
is dumb. If a container has for example the IP "1.1.1.1" and "2.2.2.2", then "hostname -I" returns "1.1.1.1 2.2.2.2" which results in INSTANCE_IP=1.1.1.12.2.2.2
Let the user choose the IP on which the space engineers server sends packets on their own.