Merge "Clean up code duplication in build_image.py." am: 514ec3b59a am: 1fd5a857e9 am: 88369ad70d

Original change: https://android-review.googlesource.com/c/platform/build/+/1835298

Change-Id: I42fd618b5a018abd57e6eab4fe4ed6ba9f70a235