core: Allow hooking before and after provisioners

lib/vagrant/action/builtin/provision.rb

@@ -68,10 +68,30 @@ module Vagrant
         # subclass and implement custom behavior if they'd like around
         # this step.
         def run_provisioner(env, name, p)
+          hook(:before_provisioner)
+
           env[:ui].info(I18n.t("vagrant.actions.vm.provision.beginning",
                                :provisioner => name))
 
           p.provision
+
+          hook(:after_provisioner)
+        end
+
+        def hook(name)
+          @logger.info("Running hook: #{name}")
+          callable = Action::Builder.new
+          action_runner.run(callable, :action_name => name)
+        end
+
+        def action_runner
+          @action_runner ||= Action::Runner.new do
+            {
+              :env     => @env[:env],
+              :machine => @env[:machine],
+              :ui      => @env[:ui]
+            }
+          end
         end
       end
     end