When the build operation starts, all the current directory
is send to Docker as a part of the build context.
The Docker Hub doesn't currently allow to configure the
path to Dockerfile, only a folder. So, when it tries to
build the image, the following error occurs:
Error build: Forbidden path: ../files.
This change copies the files/ folder as novolume/files/
and provides a Makefile to allow to update it each commit
modifying files/ using cd novolume && make update.
Fixes T787.