RFR 8196215: sun/security/util/Resources/customSysClassLoader/MessageFormatting.java failed on ar_SA locale.

[Adam Petcher]

Webrev: http://cr.openjdk.java.net/~apetcher/8196215/webrev.00/
JBS: https://bugs.openjdk.java.net/browse/JDK-8196215

Please review this minor test bug fix. The test in question ensures that 
the basic message formatting that occurs during policy initialization 
works correctly. Formatted messages are compared to the ones produced by 
the MessageFormat class. The basic formatting is intended to mimic the 
behavior of formatting in the en_US locale, but the MessageFormat object 
in the test will format messages using the default locale, which may 
cause the test to fail. This fix sets the locale to en_US in the 
MessageFormat object used in the test.