RFR: CODETOOLS-7902217: use try-with-resources where possible

[dmitry.bessonov at oracle.com]

Please review the following fix related to Automatic Resource Management 
applied to JTHarness code base.

JBS: https://bugs.openjdk.java.net/browse/CODETOOLS-7902217
Webrev: http://cr.openjdk.java.net/~dbessono/7902217/webrev/

dmitry