Revert "Return the created addon and version from Addon.from_upload, and use the return value where appropriate."

This reverts commit 180934d1f86dfa69feff6dc6828d754aaa1dc425.
Use @write for zadmin.tasks.fetch_langpacks
Merge pull request #554 from kmaglione/langpacks-task-use-db-master

Langpacks task use db master