Depend on haveged (and supply it in our repo)

Let's formalize our dependency on the haveged package.

In the DEB world it's as simple as declaring the dependency; haveged is in the main repo (at least in Jessie).

For RHEL / CentOS, the haveged package is in the EPEL repository, which not everybody is able to enable. As haveged has no non-base dependencies, can we just build it and put it in our own YUM repo?