Improving failure resiliency on view node writes.

This changeset makes it possible to retry a different view node
when no connection could be established on the first one. After
a maximum of 5 retries the operation is cancelled. The change
also makes sure that no operations are written to a node that
is currently shutting down.

Change-Id: Ie438ac667e1236aa4315008ad2dbc1ce8bde28bd
Reviewed-on: http://review.couchbase.org/24342
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>