Improve the error messages for incorrect vbucket_set
Improve the error messages for incorrect vbucket_set

Change-Id: I7e71e6f64ac712b6fcc39eda302f733ab3db9e6c
Reviewed-on: http://review.membase.org/4133
Tested-by: Dustin Sallings <1c08efb9b3965701be9d700d9a6f481f1ffec3ea@spy.net>
Reviewed-by: Dustin Sallings <1c08efb9b3965701be9d700d9a6f481f1ffec3ea@spy.net>

membase/vbucketmigrator,zbase/vbucketmigrator,zbase/vbucketmigrator,membase/vbucketmigrator,membase/vbucketmigrator,zbase/vbucketmigrator,zbase/vbucketmigrator,membase/vbucketmigrator