RFR: JDK-8055674,DIO: OUTPUT_BUFFER_EMPTY event does not fire

[Jen Dority]

issue: https://bugs.openjdk.java.net/browse/JDK-8055674
webrev: http://cr.openjdk.java.net/~jld/8055674/

Need a review for changes to fix some issues with uart event handling.

Thanks,
Jen