CBQE-1167: Backup - upgrade - restore

- Last node in the servers set doesn't participate
- If nodes are all in 1.8.1, make sure to provide
final_version
- If nodes are all in 2.0+, make sure to provide
initial_version
- Includes deletion of items before running backup-
restore

Change-Id: I7cea061a79a4824931232ca031393ca0606df43b
Reviewed-on: http://review.couchbase.org/25373
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>