RFR 8166655: JShell: Process running JShell should not be blocked from exit by non-daemon data-transfer threads

[Robert Field]

Please review --

Bug:

     JShell: Process running JShell should not be blocked from exit by 
non-daemon data-transfer threads
     https://bugs.openjdk.java.net/browse/JDK-8166655

Parent bug:

     JShell tests: jdk/jshell tests fail intermittently while cleaning 
up threads after test
     https://bugs.openjdk.java.net/browse/JDK-8163250

Related bug:

     JShell: JDIConnection leaks the input transfer thread on close
     https://bugs.openjdk.java.net/browse/JDK-8158069

Webrev:

     http://cr.openjdk.java.net/~rfield/8166655v0.webrev/

Thanks,
Robert