Revert "Revert "GC: Improve the string parsing for GC parameter setting""

This reverts commit eb980214615c49add5f77754c121d2e4c31e81ca.
Set some GC parameters only for dalvik

ART currently doesn't support setting heapminfree and heapconcurrentstart

Change-Id: I09e60802685acbec04598646e9f7700f33b53b4c
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>