RFR 8169519: JShell: Handle start-up failures and hangs gracefully

[Robert Field]

JShell: Handle start-up failures and hangs gracefully -- specifically --
Add time-outs so hangs do not lock out users and so fail-over can function.
Handle failures more gracefully, including cleaning up remote process.
Fail-fast for better user-experience and better failure handling.
Surface failure in API.
Add testing hooks.
Better failure information.

Bugs:

     8169519: JShell: Handle start-up failures and hangs gracefully
     https://bugs.openjdk.java.net/browse/JDK-8169519

     8166581: JShell: locks forever if -R options is wrong
     https://bugs.openjdk.java.net/browse/JDK-8166581

Webrev:

     http://cr.openjdk.java.net/~rfield/8169519v0.webrev/

Specdiff:

http://cr.openjdk.java.net/~rfield/8169519v0.specdiff/overview-summary.html

JShell API:

     http://cr.openjdk.java.net/~rfield/8169519v0.jshellAPI/


Thanks,
Robert