CBIDXT-100: CloseStream implemented.

- fix example app for dataport.
- changed application `opaque` type to uint16.
- feed's opaque value will increment dozen times a second, thus keeping it
  unique for a feed call and will not overflow for a long time.
- tools/multibuckets/multibuckets.go is passing.

Change-Id: I0d54d5bcc7c31fce3a371b446fc238410d1a333a
Reviewed-on: http://review.couchbase.org/42105
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>