imagebuilder: init APK dirs every time

imagebuilder: init APK dirs every time

The `--initdb` command creates basic folders required by APK,
previoiusly it would only run a single time when package_index is
actually called. Since the function isn't called if nothing changes,
`--initdb` doesn't initialize the rootfs again.

This commit moves it to package_reload, which runs every time.

Signed-off-by: Paul Spooren <mail@aparcar.org>