RFR: Bulk backports sh/jdk11 -> sh/jdk8u 2019-03-19

[Roman Kennke]

This backports recent stuff (mostly hugetlbfs/THP stuff) from sh/jdk11 
to sh/jdk8u.

Major difference is that os::pretouch_memory() doesn't take page_size 
but defaults to vm_page_size instead.

List of changes:
http://cr.openjdk.java.net/~rkennke/backports-jdk8-2019-03-19/changes.txt

Full webrev:
http://cr.openjdk.java.net/~rkennke/backports-jdk8-2019-03-19/webrev.00/

Testing: hotspot_gc_shenandoah all fine

Good?

Roman