Add backup and restore support for single instance couchbase

Given that couchbase single instance has merged, it would be nice to have backup/restore functionality.

Backup strategy:
- Save bucket metadata config (as json file) to /tmp/backups
- This is needed on restore to create the destination buckets
- Handles root enabled case by also saving /tmp/secret_key to /tmp/backups
- Use cbbackup to do the backup
- /tmp/backups will be zipped up, encrypted, and sent to Swift
- If no buckets, backup will error out

Restore strategy:
- If /tmp/backups/secret_key exists, set root password
- Iterate through bucket metadata config (json file) and use Couchbase
  REST API to create each bucket
- Wait until bucket finishes creating
- Use cbrestore (which requires destination buckets to be manually
  created first) to do the restore
- cbrestore can only restore one bucket at a time