add ebuilds for dev-db/etcd* packages and updates for app-admin/fleet package

*Documentation/examples* contains another folder called *img*. That's why ```dodoc Documentation/*``` would die and complain about that folder. ```docor -r``` will always succeed.

The *fleet.conf.sample* could also be installed to */etc/fleet/fleet.conf* since all the options are commented and therefore cause default behavor anyway.