gateway: does not stop after "Address already in use" error

[kmaehashi]

When the gateway tries to bind a port that is already used, the following error is displayed, but does not terminate automatically.

Exception in thread "main" java.net.BindException: Address already in use
        at sun.nio.ch.Net.bind0(Native Method)
        at sun.nio.ch.Net.bind(Net.java:444)
        at sun.nio.ch.Net.bind(Net.java:436)
        at sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:214)
        at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:74)
        at io.netty.channel.socket.nio.NioServerSocketChannel.doBind(NioServerSocketChannel.java:125)
        at io.netty.channel.AbstractChannel$AbstractUnsafe.bind(AbstractChannel.java:475)
        at io.netty.channel.DefaultChannelPipeline$HeadContext.bind(DefaultChannelPipeline.java:1021)
        at io.netty.channel.AbstractChannelHandlerContext.invokeBind(AbstractChannelHandlerContext.java:455)
        at io.netty.channel.AbstractChannelHandlerContext.bind(AbstractChannelHandlerContext.java:440)
        at io.netty.channel.DefaultChannelPipeline.bind(DefaultChannelPipeline.java:844)
        at io.netty.channel.AbstractChannel.bind(AbstractChannel.java:194)
        at io.netty.bootstrap.AbstractBootstrap$2.run(AbstractBootstrap.java:340)
        at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:380)
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:357)
        at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116)
        at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:137)
        at java.lang.Thread.run(Thread.java:745)