8191846: jstat prints debug message when debugging is disabled

[Per Liden]

Hi,

jstat is designed to handle the case where a perf counter doesn't exits. 
In the output jstat will then print a "-" instead of the perf counter 
value to indicate that the counter doesn't exist. However, jstat also 
prints an unnecessary message, which clobbers the output. This message 
might still be useful for debugging, but should only be printed when 
jstat is running with debug messages enabled 
(-J-DExpressionResolver.debug=true).

Webrev: http://cr.openjdk.java.net/~pliden/8191846/webrev.0/
Bug: https://bugs.openjdk.java.net/browse/JDK-8191846
Testing: hs-tier1, hs-tier2

/Per