Provide the fast-failover interval value in the terse bucket map (CCCP)

In order for couchbase clients/sdks to configure themselves when "fast-failover" settings are enabled (less than 30seconds), the setting must be made available to the client. The client will then use this value as input for its fail-over detection algorithm.

A possible name for this field could simply be "failoverInterval":

{ "rev":340,

  "name":"default",

  "failoverInterval": 5000,

   ...

}

Background:
https://docs.google.com/a/couchbase.com/document/d/1q3iausLna8RD5kupEqrD2hqEIIm7N3RPDFhX3OP33eE/edit?usp=sharing