NCBC-706: Client throws exception when first bootstrapping URI fails

When the client attempts to bootstrap, if it chooses a URI that it cannot
connect to, it should continue onto the next URI in the list and try it.
If all urls are exhausted, then the client should throw an
AggregateException which is an indication that bootstrapping as failed.

Change-Id: I49c4b619dabdc800757bb45377de556ccdb70151
Reviewed-on: http://review.couchbase.org/42594
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Simon Baslé <simon@couchbase.com>