[COOK-3960] Added LWRP for brew cask

Signed-off-by: Sean OMeara <someara@opscode.com>
[COOK-4508] Add ChefSpec matchers for homebrew_tap

Signed-off-by: Sean OMeara <someara@opscode.com>
[COOK-4566] Guard against "HEAD only" formulae

Signed-off-by: Sean OMeara <someara@opscode.com>