Updated berkshelf to 3.1.5

Updated berkshelf from 2.0.18 to 3.1.5 in Gemfile and added supermarket
source to Berksfile. Also removed sysctl from berksfile since it was
already removed from metadata in 7.0.2 and is not needed anymore.

Change-Id: I8bc2164f742df808f4f6b0f13b6bc566fafdbde3
Implements: blueprint update-berkshelf