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.
Added API endpoints for refreshing content sources

This also added more logic to the Step class to handle iterative
steps.
The new Step subclass refreshes a list of content sources.  It is called
from celery tasks.
Merge pull request #1251 from dkliban/2.5-dev

content source refresh with step reporting
Merge remote-tracking branch 'origin/2.5-dev'
Add docs on how to sign GA releases
Support catalog delete using the CLI.
Merge pull request #1274 from pulp/jortel-clear-catalog-command

Support catalog delete using the CLI.
bump release for koji rebuild
Merge branch '2.5-testing' into 2.5-dev
Merge branch '2.5-testing'
Automatic commit of package [pulp] release [2.5.0-0.15.rc].
Automatic commit of package [pulp-nodes] release [2.5.0-0.15.rc].
Merge branch '2.5-testing' into 2.5-dev
Merge branch 'master' of https://github.com/pulp/pulp
Automatic commit of package [pulp] release [2.5.0-0.16.rc].
Automatic commit of package [pulp-nodes] release [2.5.0-0.16.rc].
Merge branch '2.5-testing' into 2.5-dev
Merge branch '2.5-dev'
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.