Configure dalvik heap parameters for low memory devices

Reduces after boot memory footprint by about 5-8MB
Note: This is for low memory based devices only (~512MB RAM
or less)

Change-Id: I4b4b9ae3efaff96551457e566bbb9bd4f0f23fd5
DexOpt anything on /system in /cache/dalvik-cache

Change-Id: Id41d37047f2fcb90d513ac091dfcb85492473689

Allow property to disable dexopt on /cache

Change-Id: Ic74707c4bead387bbf82e4c6d5037efc2d2ebeaf
installd: Invert the default for dexopt-on-cache

The growth of /system apps and total /data space are making this
device-breaking (insufficient space to dexopt everything to
/cache), pointless (/data has more than enough room to hold
the cache), and in some cases, both.
The default behavior is now the same as mainline Android's: dexopt
everything to /data. Set dalvik.vm.dexopt-data-only=0 to change
that and dexopt /system apps to /cache. If you do that, make sure
your /cache can accomodate double the size of the dex classes in
system, since in some extreme cases that has been observed during
dex2oat

Change-Id: I8c793784af1fa804ccf84b442613d1000c9b7ce4