Refactor repack_super_image.py

Allow import repack_super_image from other scripts

Bug: 289369510
Test: repack_super_image --ota-tools otatools.zip \
      --misc-info misc_info.txt super.img \
      system=system.img system_ext=system_ext.img \
      product=product.img
Change-Id: Ifb8722b1d6dc9cdc4b2cd3f08a31a0171f0e539b
1 file changed