sugar: explicitly depend on dconf

dconf is needed for storing settings and configuration. and is not
declared as a dependency by the current Sugar RPMs on OLPC dropbox.

Can't rely on the Sugar RPMs, as the .spec files are apparently not
under any source control.  So add the dependency explicitly.
base: configure avahi to avoid SO_REUSEPORT

Our old kernel does not have SO_REUSEPORT, which causes avahi-daemon to
terminate on start.

This common workaround avoids that behaviour.