Updated berkshelf to 3.1.5

* Updated berkshelf from 2.0.18 to 3.1.5 in Gemfile
* Added supermarket source to Berksfile
* Pinned spiceweasel gem to 2.8
* Remove the unused knife-block gem

Change-Id: If2d801f86882fbd93b9ceb1f81f43ce7e57cbd43
Implements: blueprint update-berkshelf