Output unpacked plugin dir in addition to tar from "build-plugin" command
Output unpacked plugin dir in addition to tar from "build-plugin" command

Summary: "plugin-build" command will produce dir with unpacked plugin sources in addition to tar package. This is required because for publishing to Marketplace we need to retrieve few files from the output package, like "readme.md" and "package.json" and it's better to have it already unpacked rather than pack and then unpack to get these files.

Reviewed By: passy

Differential Revision: D28409930

fbshipit-source-id: 51c8eeb848a72850a2f126eb91a563d52851ed41

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