Added cask_env_package role to handle missing HOMEBREW_CASK_OPTS

HOMEBREW_CASK_OPTS is missing on a first run or fresh install before user's shell dotfile is patched.  Fixes things going into ~/Applications instead of /Application, lets user specify path from a playbook file, and reminds them to use cask_package in the future.

Totally stolen from rjacoby's fix for similar issue with ruby, see: https://github.com/osxc/xc-common/pull/28