Merge change 4232 into donut

* changes:
  use releasetools scripts to build update and OTA packages
tree: c06d63acd0769c978be9073979726414a54ab0a4
  1. core/
  2. libs/
  3. target/
  4. tools/
  5. buildspec.mk.default
  6. cleanspec.mk
  7. envsetup.sh