Fix ext4 size estimates

Currently, EXT4 image building is done in a 2 pass fashion:

First pass: build ext4 image with small margin/headroom, check the
number of block used in the output image

Second pass: Build ext4 image again with an estimated block count from
first pass

The two pass implementation is done to keep image size at a
minimum. Recently some failures in first pass invocation is observed due
to image being undersized. Since we will reduce the image size in 2nd
pass, it's OK to increase the image size estimate during first pass. Add
a headroom 10% of total file size to fix build failures.

Test: cherry pick r.android.com/q/topic:%22aosp_cf_system_x86_64%22 and
m aosp_cf_system_x86_64

Bug: 321003625
Change-Id: I254310c67a08b98b05d2c858d4ab59a48112a07b