Don't start a failout chain if NMVB config can't be parsed

This change will suppress any errors for a failed not-my-vbucket
response so that the server won't be punished for not sending us a
config

Change-Id: I134dafdf444478870cdb79bd1ceef04c3be6ee63
Reviewed-on: http://review.couchbase.org/31037
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>