Add a zero-fill flag to ImageManager::CreateBackingImage.

libsnapshot will need COW devices to be zeroed on creation. Since ImageManager knows whether the image is already zero-filled or not, it makes sense to have the logic here.

Bug: 134536978
Test: libsnapshot_test gtest
Change-Id: I2405e163cc1afe97f7d5e86419a325a4bf5bf524
5 files changed