Disable sparse image for GSI products

There are a couple of use cases where we don't want sparse image:
1. `DynamicSystemInstallationService` in Q framework doesn't support
   sparse images.
2. Super image manipulation tools (like `lpadd`) doesn't play nice with
   sparse images.

Force non-sparse GSI so we don't break backwards compatibility (1) and
we don't need to write `simg2img` everywhere (2).

Bug: 167695592
Test: Prepare a device flashed with Q framework
Test: Build system.img and create system.img.zip; the image is non-sparsed
Test: m tradefed-all && \
  tradefed.sh run commandAndExit template/atest_local_min \
  --template:map preparers=template/preparers/dsu-preparer \
  --extra-file system-img.zip=out/.../system.img.zip \
  --dynamic-system-update:disable-tear-down
Change-Id: Ib7667165ce53e87eb86bc7d3f56c80a418123a62