Allow compatibility with Berkshelf 2.X and 3.X

moved mkdir -p .cookbooks to be only run if not berks 3 because berks
vendor fails when it tries to create .cookbooks and it already exists

Change-Id: I915859c1925fe06771f53c94094b70b086f647b0
Implements: blueprint update-berkshelf
Merge "Allow compatibility with Berkshelf 2.X and 3.X"