When merging two arrays during deep merge:

  If merge is happening across the precedence levels (i.e. default, override, etc...)
     Pick the array from the higher precedence level
  If merge is happening at the same precendence level (i.e. when we are merging role default attribute with node default attributes)
     Concatanate the arrays.
Specs for the intended behavior of CHEF-4631.
Config option to restore previous array merging behavior in deep_merge when needed.
Fix a comment.
Merge pull request #1118 from opscode/CHEF-4631

CHEF-4596 / CHEF-4631 : Pick the array that is higher in the precedence order instead of merging during deep merge