units: set TimeoutSec on some oneshot services

Services which are not crucial to system bootup, and have Type=oneshot
can effectively "hang" the system if they fail to complete for whatever
reason. To allow the boot to continue, kill them after a timeout.

In case of systemd-journal-flush the flush will continue in the background,
and in the other two cases the job will be aborted, but this should not
result in any permanent problem.

(cherry picked from commit 0775b9b611)

units/systemd-backlight@.service.in

@@ -19,3 +19,4 @@ Type=oneshot
 RemainAfterExit=yes
 ExecStart=@rootlibexecdir@/systemd-backlight load %i
 ExecStop=@rootlibexecdir@/systemd-backlight save %i
+TimeoutSec=2min

units/systemd-journal-catalog-update.service.in

@@ -18,3 +18,4 @@ ConditionNeedsUpdate=/etc
 Type=oneshot
 RemainAfterExit=yes
 ExecStart=@rootbindir@/journalctl --update-catalog
+TimeoutSec=2min

units/systemd-journal-flush.service.in

@@ -19,3 +19,4 @@ RequiresMountsFor=/var/log/journal
 ExecStart=@rootbindir@/journalctl --flush
 Type=oneshot
 RemainAfterExit=yes
+TimeoutSec=2min