JDK 10 RFR of JDK-8181309: Refactor shell test AsynchronousChannelProvider/custom_provider.sh to java

[Amy Lu]

java/nio/channels/spi/AsynchronousChannelProvider/custom_provider.sh

Please review this patch to refactor the shell test to java.

bug: https://bugs.openjdk.java.net/browse/JDK-8181309
webrev: http://cr.openjdk.java.net/~amlu/8181309/webrev.00/

Thanks,
Amy