1145723 - log startup message 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 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.
1111228 - Fix API doc typo.

https://bugzilla.redhat.com/show_bug.cgi?id=1111228
1135589 - move PRIMARY_ID definition

The PRIMARY_ID constant was defined in model.py which also attempted to read
`server.conf` for database connection info. This meant that pulp-admin required
access to `server.conf`.

I moved PRIMARY_ID to pulp.common.constants so it can be imported without
pulling in other code.
Merge pull request #1279 from pulp/fix-nodes-import

1135589 - move PRIMARY_ID definition
Merge branch '2.5-testing' into 2.5-dev
Merge pull request #1259 from beav/init.d-logging

1145723 - log worker startup/shutdown messages in Celery logs