8210013: jcmd VM.symboltable might return "statistics unavailable at this moment"

[Leonid Mesnik]

Hi

Could you please review following fix which add "statistics unavailable"string as a valid output for VM.symboltable for JcmdStressModule in Kitchensink. 
The goal of module is to make only sanity check of output. So test doesn't track how often jcmd couldn't get data for VM.symboltable. 

webrev: http://javaweb.us.oracle.com/~lmesnik/webrev/8210013/webrev.00/ <http://javaweb.us.oracle.com/~lmesnik/webrev/8210013/webrev.00/>
bug: https://bugs.openjdk.java.net/browse/JDK-8210013 <https://bugs.openjdk.java.net/browse/JDK-8210013>

Leonid