Add helpers for deployments without roles

[BattleBrisket]

No matter how my deployment roles lay out for production and staging, I always have one or two environments (development, and occasionally a demo server) that put all the roles on a single instance. In those cases, roles are effectively meaningless.

Initially I would handle those situations by writing conditionals in my rake tasks that look like this...

if role? :www || ENV['WD_ROLES'] == ''

...but that exposes WhiskeyDisk internals within my rake tasks. The conditionals also get a bit uglier when trying to watch for interesting file changes...

if (role?(:db) || ENV['WD_ROLES'] == '') and changed?('db/migrate')

So I added some helpers that encapsulate the notion, "Is this a deployment without any roles at all?"

no_roles? returns true if the ENV['WD_ROLES'] definition is empty.

nothing_or_role?(role) returns true if the current deployment has the specified role, or if the ENV['WD_ROLES'] definition is empty.