Add `haveged` install to docker one-click

[banagale]

Add haveged to the standard set of apt-get packages in the packer template.

The current ubuntu 20.04 docker 1-click template can not run docker-compose reliably on the Digital Ocean Basic Regular Intel Droplet.

In my experience, docker-compose will regularly, silently lock up the droplet with no indication as to what is wrong.

This is due to lack of a sufficient entropy pool as described by Digital Ocean as far back as 2013.

While there are ways to interact with DO to customize the docker 1-click on a case-by-case basis, this is beyond the expected scope of someone new to working with DO.

While I personally think docker-compose should at least issue a warning and explanation, Docker's position is ~that this is an OS-level concern.