launch_daemon: fix check for existing directory

BEntry.InitCheck returns B_OK even if the leaf does not exist. So the
code in launch daemon to create directories (/tmp and
/var/shared_memory) was never run.

Fixes #12760.

launch_daemon: Initialize /tmp & /var/shared_memory, clock.

* Added initializing /tmp & /var/shared_memory to the launch_daemon.
* Moved clockconfig.cpp code into the launch_daemon.
* This follows systemd design; since those jobs are fixed, it doesn't
matter where you maintain them.
* The init jobs are BJobs, but the JobQueue is only used for that
one use for now. At a later time, I intend to put the job launching
in there, as well. BJob allows to represent the dependencies already.

launch_daemon: Initialize /tmp & /var/shared_memory, clock.

* Added initializing /tmp & /var/shared_memory to the launch_daemon.
* Moved clockconfig.cpp code into the launch_daemon.
* This follows systemd design; since those jobs are fixed, it doesn't
matter where you maintain them.
* The init jobs are BJobs, but the JobQueue is only used for that
one use for now. At a later time, I intend to put the job launching
in there, as well. BJob allows to represent the dependencies already.