Use GSI-specific init script to detect GSI image. am: 9772f86fb7

Original change: https://android-review.googlesource.com/c/platform/system/gsid/+/3206391

Change-Id: Ie07772bb98bfb61b8672818a37a89b09a6edf49a
Signed-off-by: Automerger Merge Worker <[email protected]>