Jenkins charm volume-map totally fails to operate properly with persistent storage.

[Robert Bruce Park]

The Jenkins charm has a serious issue preventing persistent volumes from being reusable across instances of jenkins.

Steps to reproduce:

1. Deploy a jenkins instance.

2. Use volume-ephemeral-storage and volume-map options to mount a fresh persistent volume into jenkins.

3. Observe that persistent storage is being utilized and jenkins is functioning.

4. Destroy juju environment, re-bootstrap, re-deploy, re-attach persistent volume.

5. Observe that jenkins appears to work at first (records of previously run jobs exist), but then if you try to view the console output of a job or try to sign in with SSO, you get this traceback:

http://paste.ubuntu.com/11845262/

Previously, the workaround I would use for this bug would look like this:

1. Generate a fresh nova volume *every* *time* (effectively meaning "persistent" nova volumes were single-use only).

2. Rsync just mission-critical files from one nova volume to the other, letting jenkins treat each volume like a fresh installation.

This was of course a lot of trouble as I'd have to pick and choose which files from /var/lib/jenkins to rsync.

The new workaround which is much easier is to simply delete /var/lib/jenkins/secrets directory after mounting the volume, then re-run jenkins charm install hook. Apparently each new instance of jenkins must generate it's own /var/lib/jenkins/secrets directory and if you try to re-use this directory from a previous instance of jenkins, you get the above traceback.