RFR 8158174: jshell tool: leaks threads waiting on StopDetectingInputStream

[Jan Lahoda]

Hello,

Bug:
https://bugs.openjdk.java.net/browse/JDK-8158174

Webrev:
http://cr.openjdk.java.net/~jlahoda/8158174/webrev/index.html

The fix is to stop the StopDetectingInputStream when closing the 
ConsoleIOContext. I chose "shutdown" for the name of the method, mostly 
to be consistent with ConsoleReader.shutdown().

Any feedback is welcome!

Thanks,
     Jan