Allow semi-static bootstrapping

I'm marking this as critical because many folks seem to frown upon the high delays (read http connection latency) when establishing a new couchbase client.

In this case, this would be a constructor option available for lcb_create which will accept an opaque 'map file'. This 'map file' will really just be a dump of a vbucket configuration. What makes this different from compat mode is that the clients will bootstrap when a network error or timeout occurs.

However in the normal model of spawn -> mc operation, where the cluster config is fairly static, there is no need for the latency induced by an extra http connection.

We'd need to implement file-locking semantics to write to this file (we'd maybe just ask for a path to read/write the config to/from, perhaps checking the timestamp, too).. as we'd have multiple clients trying to read/write to this. This is simple enough in Unix

This is in conjunction with a different discussion regarding how to best handle re-bootstrapping, where it was suggested that we really don't need the bootstrap connection in the first place.

There are inherent risks involved with this approach, for example, if one specifies the wrong nodes, then we only know about this during the re-bootstrap.