yarn cleaninstall from Docker image

Summary:
For proper build caching, we want to first handle the node_modules, and then later copy in the actual files.

Depends on D3712

Test Plan: Make sure I can build the Node.js keyserver from Docker

Reviewers: palys-swm, jimpo

Reviewed By: palys-swm, jimpo

Subscribers: Adrian, atul, karol-bisztyga, benschac, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3713