RFR (S) 8232051: Epsilon should warn about Xms/Xmx/AlwaysPreTouch configuration

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8232051

This is arguably the UX bug: users expect low latency, but may not be aware that additional
configuration is needed for GCs to perform well in those conditions. Epsilon already enables LSM,
and should warn about Xms/Xmx/AlwaysPreTouch config too. It cannot adjust these settings, though,
because it would affect startup time -- users would have to opt-in.

Fix:
  https://cr.openjdk.java.net/~shade/8232051/webrev.01/

Testing: Linux x86_64 {fastdebug, release} gc/epsilon; jdk-submit (running)

-- 
Thanks,
-Aleksey