image: Use $BUILD_DIR variable instead of deriving it from $BASE_DIR a second time
image: Move modules file to the correct location
image: Don't copy kernel modules to the prepared root-fs, but copy them directly to the mounted image

This is one step towards splitting the root-fs generation and the image generation into two scripts.
image: Add stress package
image: Add $ACP_CMD variable
image: Boot from MMC0 again