Allow overriding COW version in host-side cow_converter am: e7ca36910b

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2886532

Change-Id: I06b216516634c3997ea2418f4aa32ae85b5a608b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>