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From Shawn Heo's patch:

Ext4 introduced reserved clusters to prevent costly zeroout, or
unexpected ENOSPC. The size is 2% or 4096 clusters, whichever
is smaller (http://lwn.net/Articles/546473/).

So, we need to allocate additionally this amount of free space
to asecs when vold create asec images. This is required when
Android runs on Linux kernel 3.10 or later.

see: https://android-review.git.corp.google.com/#/c/96160



Change-Id: Iacff16b8cf0314493c355fa741bcfa519f744d6c
Signed-off-by: Daniel Rosenberg <drosen@google.com>