retryq: Hide not-my-vbucket return codes

This is rather unfortunate, however currently most applications do not
have codepaths handling this error.

Change-Id: Ic076d9450fe59f4d714c822d956a14242d9bd31f
Reviewed-on: http://review.couchbase.org/39925
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>