integ-cli: fix TestImportDisplay & add FileServer

This PR fixes TestImportDisplay. HTTPS handshakes are failing erratically sometimes and that's breaking TestImportDisplay.

This PR moves the download of the file to the Dockerfile and TestImportDisplay simply imports it from a local server which serves files over HTTP.
Also, may be makes sense (for avoid all this edge cases) to copy needed files to needed paths in some tmp dir and use 
```
httptest.Server(http.FileServer(http.Dir(tmpdir)))
```