Couchbase restore fails when restoring on a smaller flavor

The current implementation tries to preserve all bucket information
including memory quota (and number of bucket replicas). This will only
work when restoring onto a flavor with the same general spec as the source.

It will cause the quota to be unnecessarily low on larger flavors
and/or prevent the service from starting on smaller flavors
(i.e. "RAM quota specified is too large to be provisioned into this cluster.").

The quota should be recomputed based on the target instance's flavor.