JDK 9 RFR of 8067964: Native2ascii doesn't close one of the streams it opens

[Brian Burkhalter]

Please review at your convenience.

Issue:  https://bugs.openjdk.java.net/browse/JDK-8067964
Patch:  http://cr.openjdk.java.net/~bpb/8067964/webrev.00/

Summary:

Use try-with-resources statements to manage AutoCloseables in 
sun.tools.native2ascii.Main.convert(). Also clean up code formatting of the 
method and remove unneeded import statements.

Thanks,

Brian