Review request: 8009813 NMT should wait all collected data to be processed before generates report when PrintNMTStatistics option is specified

[Zhengyu Gu]

This is a simple change that has NMT to wait for collected data to be 
processed, before it prints out tracking data at JVM exit when 
PrintNMTStatisitcs option is specified.

Without the wait, the data can be empty for short-lived application, or 
might not match the data collected through other methods.

JBS: https://jbs.oracle.com/bugs/browse/JDK-8009813
Webrev: http://cr.openjdk.java.net/~zgu/8009813/webrev.00/

Test:
   - JPRT
   - vm.quick.testlist on Linux 32


Thanks,

-Zhengyu