systemd: RemainAfterExit in openafs-client.service

systemd: RemainAfterExit in openafs-client.service

Currently, if the client is started without any options that require
an extra thread (like -afsdb), all processes spawned by afsd will
exit. There may be some kernel threads still active, but those are
spawned by the kernel module, and are not child processes of the
parent afsd process, or anything like that.

Since we are a Type=forking service in systemd, systemd interprets
this situation to mean that the service has stopped successfully, and
then runs the ExecStop commands. So, for example, if our AFSD_ARGS in
our sysconfig is "-fakestat -afsdb", the service starts as normal. But
if it is changed to "-fakestat", then when openafs-client.service is
started, it immediately stops again.

To avoid this, turn on the systemd option RemainAfterExit, which tells
systemd that the service has not stopped if all of our processes have
exited. The client service will thus remain running until it is
stopped.

Issue reported by Rich Sudlow.

FIXES 133482

Reviewed-on: http://gerrit.openafs.org/11440
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Anders Kaseorg <andersk@mit.edu>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit cb8195d2d6ce1c01e132c05c1bf5593eab45b2c6)

Change-Id: I4005d5dabae8ef72194938475cf46f5bc1f222f8
Reviewed-on: https://gerrit.openafs.org/12481
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>