[13u] RFR 8241638: launcher time metrics always report 1 on Linux when _JAVA_LAUNCHER_DEBUG set

[Dmitry Cherepanov]

JBS: https://bugs.openjdk.java.net/browse/JDK-8241638
original patch: https://hg.openjdk.java.net/jdk/jdk/rev/3f8d03880bf5
webrev for 13u: 
http://cr.openjdk.java.net/~dcherepanov/openjdk13u/8241638/webrev.v0/

The patch applies cleanly except the change in LauncherCommon.gmk due to 
different context (context changed after 8233410), re-applied this part 
manually.

Thanks,

Dmitry