Update to Xenial image and fix docker config commands

Vagrantfile

@@ -1,5 +1,5 @@
 Vagrant.configure(2) do |config|
-  config.vm.box = "ubuntu/trusty64"
+  config.vm.box = "ubuntu/xenial64"
   config.vm.hostname = "docker-ubuntu16"
   config.vm.provision "shell", path: "provision.sh"
   config.vm.provider "virtualbox" do |v|

provision.sh

@@ -4,12 +4,8 @@ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -
 add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
 apt-get update
 apt-get install -y docker-ce
-usermod -a -G docker vagrant
-mkdir -p /etc/docker
-cat << EOF > /etc/docker/daemon.json
-{
-	"hosts": ["unix:///var/run/docker.sock", "tcp://0.0.0.0:2376"]
-}
-EOF
+usermod -a -G docker ubuntu
+sed -i 's$fd://$fd:// -H tcp://0.0.0.0:2376$g' /lib/systemd/system/docker.service
+systemctl daemon-reload
 service docker restart
 apt-get clean