Merge change 488 into donut

* changes:
  add -n option to turn off prereq check when build OTA packages
tree: 04905272f9b98017e0d667649c706f0f7d7f385d
  1. core/
  2. libs/
  3. target/
  4. tools/
  5. buildspec.mk.default
  6. cleanspec.mk
  7. envsetup.sh