Docker proxy config doesn't work on Ubuntu 15.04

lib/vagrant-proxyconf/cap/debian/docker_proxy_conf.rb

@@ -0,0 +1,50 @@
+require_relative '../util'
+
+module VagrantPlugins
+  module ProxyConf
+    module Cap
+      module Debian
+        # Capability for docker proxy configuration
+        module DockerProxyConf
+          CONFIG_DIR = '/etc/default/'
+
+          # @return [String, false] the path to docker or `false` if not found
+          def self.docker_proxy_conf(machine)
+            docker_command = find_docker_command(machine)
+            return false if docker_command.nil?
+
+            config_path = CONFIG_DIR + docker_command
+            return config_path unless Util.which(machine, 'systemctl')
+
+            machine.communicate.tap do |comm|
+              src_file = "/lib/systemd/system/#{docker_command}.service"
+              dst_file = "/etc/systemd/system/#{docker_command}.service"
+              tmp_file = "/tmp/#{docker_command}.service"
+              env_file = "EnvironmentFile=-\\/etc\\/default\\/#{docker_command}"
+              if comm.test("grep -q -e '#{env_file}' #{src_file}")
+                comm.sudo("cp -p #{src_file} #{tmp_file}")
+              else
+                comm.sudo("sed -e 's/\\[Service\\]/[Service]\\n#{env_file}/g' #{src_file} > #{tmp_file}")
+              end
+              unless comm.test("diff #{tmp_file} #{dst_file}")
+                # update config and restart docker when config changed
+                comm.sudo("mv -f #{tmp_file} #{dst_file}")
+                comm.sudo('systemctl daemon-reload')
+              end
+              comm.sudo("rm -f #{tmp_file}")
+            end
+            config_path
+          end
+
+          private
+
+          def self.find_docker_command(machine)
+            return 'docker'    if Util.which(machine, 'docker')
+            return 'docker.io' if Util.which(machine, 'docker.io')
+            nil
+          end
+        end
+      end
+    end
+  end
+end

lib/vagrant-proxyconf/capability.rb

@@ -18,6 +18,11 @@ class Plugin < Vagrant.plugin('2')
         Cap::CoreOS::DockerProxyConf
       end
 
+      guest_capability 'debian', 'docker_proxy_conf' do
+        require_relative 'cap/debian/docker_proxy_conf'
+        Cap::Debian::DockerProxyConf
+      end
+
       guest_capability 'linux', 'env_proxy_conf' do
         require_relative 'cap/linux/env_proxy_conf'
         Cap::Linux::EnvProxyConf