run.sh script disables IPv6 on Linux

The run.sh contains a bug that disabled IPv6 on Linux systems providing a no longer valid reason for EAP 5:

• JDK 1.5 and lower is NOT supported with EAP 5!
• it ignores exported JAVA_OPTS
• there is JDK 1.6 for Linux system which supports IPv6 correctly

If we still want to disable IPv6 by default:

• the comments needs to state a proper reason
• documentation should consistently document why is that the default and how to re-enable

1. Force IPv4 on Linux systems since IPv6 doesn't work correctly with jdk5 and lower
   if [ "$linux" = "true" ]; then
   JAVA_OPTS="$JAVA_OPTS -Djava.net.preferIPv4Stack=true"
   fi