Failed restore juju.txns.stash 'collection already exists'

[Martin Packman]

A backup-restore run in CI failed with "juju.txns.stash: error running create command: collection already exists".

<http://reports.vapour.ws/releases/issue/578fdcfa749a5622eb5d5a5f>
<http://reports.vapour.ws/releases/4155/job/functional-backup-restore-xenial/attempt/318>

2016-07-20 19:13:23 ERROR juju.api.backups restore.go:143 could not clean up after failed restore attempt: cannot complete restore: <nil>: juju restore is in progress - Juju api is off to prevent data loss
2016-07-20 19:13:23 ERROR cmd supercommand.go:458 cannot perform restore: <nil>: restore failed: error restoring state from backup: error restoring database: error executing "/usr/lib/juju/mongo3.2/bin/mongorestore":
... reading metadata for juju.txns.stash from /tmp/juju-backups-967945345/juju-backup/dump/juju/txns.stash.metadata.json; 2016-07-20T19:13:21.823+0000 [########################] juju.providerIDs 209.0 B/209.0 B (100.0%); 2016-07-20T19:13:22.282+0000 finished restoring juju.storageconstraints (1 document); 2016-07-20T19:13:22.283+0000 [########################] juju.providerIDs 209.0 B/209.0 B (100.0%); 2016-07-20T19:13:22.283+0000 restoring indexes for collection juju.providerIDs from metadata; 2016-07-20T19:13:22.295+0000 Failed: juju.txns.stash: error creating collection juju.txns.stash: error running create command: collection already exists;

[Anastasia (anastasia-macmood)]

This appears to be fixed in 2.1 and develop (2.2).

The original problems have only been reported against master and a feature branch branched from master.

Targeting to currently active milestone.