cbbackupmgr should lock at the repo level instead of the archive level

Currently cbbackupmgr has a lockfile at the archive level to avoid multiple cbbackupmgr process accessing an archive at the same time. We should move this lock to the repo level so that multiple processes can be active an a single archive (as long as they are accessing different sets of data).

This will require some changes to the logging since logs are stored at the archive level (therefore, they will also have to be moved).

Possible issues/concerns

Where do we store the logs?
The easy option for this is to just move the logs directory down a level, however, we should think ahead because at some point we may end up moving the logs once again. There have been talks about moving the logfile into the backup itself since it kind of "belongs" to that backup. This has issues itself because we setup logging very early on, and don't create the backup directory (for a backup) until a fair bit later. We'd need to consider what affect this might have.