It is essential that the gettys are proper dependencies from
getty.target so that they aren't killed and immediately restarted on
runlevel changes. Hence rework the logic to implicitly add console
gettys to getty.target as dependencies.
This also adds an automatic hvc console for virtualizers.
https://bugzilla.redhat.com/show_bug.cgi?id=501720
In order to simplify writing of unit files introduce default
dependencies that are added to all units unless explictly disabled in a
unit. This option can be switched off for select units that are involved
in early boot-up ot late system shutdown,
This should simplify service files for most normal daemons, but breaks
existing service files for software involved in early boot (notably
udev), which need to be updated for a DefaultDependencies=no setting)
