RFR 8228589: BasicJStackTest.java and JcmdOutputEncodingTest.java failing after JDK-8227868

[Schmelter, Ralf]

The tests included to check the correct UTF-8 conversion of jstack/jinfo/jcmd will fail, if the platform encoding cannot represent the Unicode characters we used in the code. These characters will be correctly converted by the tools, but when printed out on System.out, the PrintSteam has to convert the chars to bytes. And if a Unicode character is not supported by the platform encoding, a question mark is used instead. 

This is what happened on some machines the test was run. To fix this, we now set the encoding used to UTF-8 explicitly. I had to adapt some test library code to add the option of using a specific charset for the conversion from bytes to chars.

webrev: http://cr.openjdk.java.net/~rschmelter/webrevs/8228589/webrev.0/
bugreport: https://bugs.openjdk.java.net/browse/JDK-8228589

Best regards,
Ralf