Summary: G1ElasticHeap to support heap shrink/expansion in runtime

Test Plan:
test/elastic-heap/

Reviewers:

Issue:
https://github.com/alibaba/dragonwell8/issues/46

CR:
https://github.com/alibaba/dragonwell8_hotspot/pull/12

Summary: Allow use of large pages for auxiliary data structures in G1. Clean up existing interfaces.
Reviewed-by: jmasa, pliden, stefank

8062063: Usage of UseHugeTLBFS, UseLargePagesInMetaspace and huge SurvivorAlignmentInBytes cause crashes in CMBitMapClosure::do_bit
Summary: Making sure committed memory is cleared when re-committed, even if using large pages.
Reviewed-by: jwilhelm, tschatzl

8062063: Usage of UseHugeTLBFS, UseLargePagesInMetaspace and huge SurvivorAlignmentInBytes cause crashes in CMBitMapClosure::do_bit
Summary: Making sure committed memory is cleared when re-committed, even if using large pages.
Reviewed-by: jwilhelm, tschatzl

Summary: If large pages are enabled and configured in Linux, the VM always pre-commits the entire space. The VM fails verification of the commit of the initial heap because some internal data structure marked all memory pages of the heap as committed during initialization. This makes the code think that we attempted a double-commit during first allocation of the heap. Remove the initial marking of memory pages of the heap to committed.
Reviewed-by: mgerdin

Summary: Allow G1 to decommit memory of arbitrary regions within the heap and their associated auxiliary data structures card table, BOT, hot card cache, and mark bitmaps.
Reviewed-by: mgerdin, brutisso, jwilhelm

Summary: Factor out pretouch code of the various virtual space management classes and use them everywhere including in G1.
Reviewed-by: stefank, ehelin, dholmes