8168615: JShell API: jdk.jshell.spi should be a pluggable ServiceLoader SPI
Reviewed-by: jlahoda

8169519: JShell: Handle start-up failures and hangs gracefully
8166581: JShell: locks forever if -R options is wrong
8169234: JShell: hangs on startup on some computers caused by hostname
Reviewed-by: jlahoda

8161983: JShell API: Clean-up following 8160127 et. al.
Reviewed-by: jlahoda