RFR 8243489: Thread CPU Load event may contain wrong data for CPU time under certain conditions

[Jaroslav Bachorík]

Please, review the following backport

JIRA.    : https://bugs.openjdk.java.net/browse/JDK-8243489
Webrev: http://cr.openjdk.java.net/~jbachorik/8243489/8u/hotspot/webrev/


The backport applies cleanly but the accompanying test had to be
dropped because it is using gTest and MockOs facilities which are not
available in JDK8u. Recreating the test without MockOs is near to
impossible because it is relying on being able to modify the reported
thread CPU time to assert the correct functionality.

Cheers,

-JB-