1145723 - log worker startup/shutdown messages in Celery logs

On RHEL6, Pulp's init.d scripts invoke celery in a way that creates log files
under `/var/log/pulp/` that are not used during normal operation. This causes
confusion for users since they think the logs are going to be there instead of
to `/var/log/messages`.

The init.d scripts have been modified to print startup/shutdown messages in
these logs, and direct users to `/var/log/messages` for more information.

I did not add "startup" to the log filenames in case a user is already
collecting logs from their existing locations.
Doesn't restart just call stop then start? If that's true, those might already write logs. Also, this might not be safe if it tries to write at the same time as the startup logs.