NCBC-591: NRE in HttpStreamingProvider.GetBucketConfig

Change-Id: Icddb5955d12a2dbf749574dd25c8875491414818
Reviewed-on: http://review.couchbase.org/40742
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Brett Lawson <brett19@gmail.com>