RFR (XS) JDK-8153582 Logging of ConcGCThreads is done too early

[Joseph Provino]

Please review this very small change to log ConcGCThreads
and ParallelGCThreads correctly.

Webrev:  http://cr.openjdk.java.net/~jprovino/8153582/webrev.00

CR: JDK-8153582Logging of ConcGCThreads is done too early 
<https://bugs.openjdk.java.net/browse/JDK-8153582>

Messages look like below.

java -Xlog:gc=trace -XX:+PrintFlagsFinal -version

[0.002s][trace][gc] MarkStackSize: 4096k  MarkStackSizeMax: 16384k
[0.038s][trace][gc] ConcGCThreads: 5
[0.039s][trace][gc] ParallelGCThreads: 18
[0.056s][info ][gc] Using G1

java  -Xlog:gc=trace -XX:+PrintFlagsFinal -XX:+UseConcMarkSweepGC -version

[0.002s][trace][gc] MarkStackSize: 4096k  MarkStackSizeMax: 524288k
[1.001s][trace][gc] ConcGCThreads: 5
[1.001s][trace][gc] ParallelGCThreads: 18
[1.015s][info ][gc] Using Concurrent Mark Sweep