CBQE-0: get vBucketMap if there is no VBucketMapForward

Change-Id: Ifb9e2a6c2977ea0657bda8f37d31a7bbb8621209
Reviewed-on: http://review.couchbase.org/31360
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>