moving conditional attributes to a recipe

Some users, such as myself, only set attributes in an attributes file and/or recipe. We do not use roles or environments to set attributes. If conditions in an attributes file are determined before a recipe is compiled and before other attribute recipes are considered.

At this point it is impossible to set default['postfix']['virtual_alias_domains'] without using the role or environment for an override. This change is set to resolve this issue and allows the ability to override attributes through other attributes file and/or recipes.