Umbra task for refactoring java/nio shell cases to java. 12 in total

jdk/test/java/nio/Buffer/LimitDirectMemory.sh
jdk/test/java/nio/channels/AsynchronousChannelGroup/run_any_task.sh
jdk/test/java/nio/channels/Selector/lots_of_updates.sh
jdk/test/java/nio/channels/SocketChannel/Open.java (which runs @run shell Open.sh)
jdk/test/java/nio/channels/spi/AsynchronousChannelProvider/custom_provider.sh
jdk/test/java/nio/channels/spi/SelectorProvider/inheritedChannel/run_tests.sh
jdk/test/java/nio/charset/Charset/default.sh
jdk/test/java/nio/charset/coders/CheckSJISMappingProp.sh
jdk/test/java/nio/charset/spi/basic.sh 
jdk/test/java/nio/file/Files/delete_on_close.sh
jdk/test/java/nio/file/Files/walkFileTree/find.sh
jdk/test/java/nio/file/Path/MacPathTest.java (which runs @run shell MacPathTest.sh)