restrict cost_price to admin users through the api
Merge branch 'api_hide_cost_price' of github.com:godaddy/spree into godaddy-api_hide_cost_price
Load current user roles on api requests
Add admin flag on variants related cache template

We want to make Variant#cost_price only available for admins so we need
to make sure difference cache keys are set as per current user role
otherwise the first template cached would decide whether or not the
attribute would be available (rather than the user role itself)