pkgadmin: Use systemd.timer instead of cron

Now that many workstations are switched off during nighttime, we have
the problems that these don't pull new packages.

Use systemd.time and utilize `Persistent=true` to catch up on missed
events at boot time. Also use `RandomizedDelaySec=2 hours` to avoid
overloading the fileserver or the network when a new big package is
going to be pulled by all systems.

install.sh

@@ -152,7 +152,8 @@ install_exec prun/ptype                                  "$DESTDIR$usr_bindir/pt
 install_exec prun/pman                                   "$DESTDIR$usr_bindir/pman"
 install_exec put_websafe/put_websafe                     "$DESTDIR$usrlocal_bindir/put_websafe"
 install_exec pkgadmin/pkgadmin                           "$DESTDIR$usr_sbindir/pkgadmin"
-install_cron pkgadmin/crond-pkgadmin-update              "$DESTDIR$crond_dir/pkgadmin-update"
+install_data pkgadmin/pkgadmin-update.service            "$DESTDIR$systemdunitdir/pkgadmin-update.service"
+install_data pkgadmin/pkgadmin-update.timer              "$DESTDIR$systemdunitdir/pkgadmin-update.timer"
 install_exec mxraid/mxraid                               "$DESTDIR$usr_sbindir/mxraid"
 install_exec mxraid/mxraid_assemble                      "$DESTDIR$usr_sbindir/mxraid_assemble"
 install_data mxraid/mxraid.service                       "$DESTDIR$systemdunitdir/mxraid.service"

pkgadmin/pkgadmin-update.service

@@ -0,0 +1,2 @@
+[Service]
+ExecStart=pkgadmin update

pkgadmin/pkgadmin-update.timer

@@ -0,0 +1,7 @@
+[Timer]
+OnCalendar=2:00
+RandomizedDelaySec=2 hours
+Persistent=true
+
+[Install]
+WantedBy=timers.target