Handle View Errors (Vbucket & Merge) appropriately

During rebalance out it can happen that the view node is still able to service http connections, but fails with the following errors:

- error Reason: A view spec can not consist of merges exclusively.
or
- no_active_vbuckets Reason: Cannot execute view query since the node has no active vbuckets

If this is happening, the client needs to deal with it. Appropriate solution needs still to be dicussed, but one approach could be to retry on a different node. Note that this needs to work for both async and sync calls.