To allow users to continue to use the community plugin, this commit adds
a switch that will not load the core trigger feature if it detects the
community plugin is installed. It also allows the user to disable the
warning so they can continue to use the plugin without extra output.
This works by registering a `config` with `:provider => true` with the
same name as your provider. Vagrant will then automatically configure
the provider when `config.vm.provider` is used.
Brian Cain
Seth Vargo
Mitchell Hashimoto