1109430 - goferd controlled by systemd

https://bugzilla.redhat.com/show_bug.cgi?id=1109430

Changes:
- Update to gofer 1.3.0.
- Get rid of references to pulp-agent in docs.
- Add systemd examples in docs for goferd.
- Update 2.4 release notes that pulp-agent is no longer being symlinked.