services: Adjust service dependencies

Previously firstboot (and others) depended on systemd services or
targets which could go down during the original's service runtime.
Because some target service would depend on a service it would bring
down, systemd would also kill the target service (because a dependency
wasn't met anymore).

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=983547
Change-Id: I0596c054cd996d10032f737a8fcc010d60254bf0
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>