MB-11917: Use existing OTP fork

Instead of using/having another OTP fork in the Couchbase Labs account,
use the existing one and point to the specific branch.

Change-Id: Iceb147ecf557f41d8586bd64ca7c21a21d5a4e22
Reviewed-on: http://review.couchbase.org/44014
Tested-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Chris Hillery <ceej@couchbase.com>