Adjust dockerfile and docker-build steps

- Now that sourcing requires, board/ for the bsp, we need to
pull this into the container. So copy board/build into a temporary
folder, and place the Dockerfile alongside them. The rest of the setup
we run to make the container is unchanged.
- Add some dependencies to docker-build target, so that it properly
regenerates if a new prerequisite or the like is added.

Change-Id: I56afdc5fcef52f4029e1745c815265a0bfc8ed9b
2 files changed