providers/docker: `vagrant ssh` proxies through the host VM

plugins/providers/docker/action.rb

@@ -162,6 +162,8 @@ module VagrantPlugins
                 b3.use Message, I18n.t("docker_provider.messages.not_running")
                 next
               end
+
+              b3.use PrepareSSH
               b3.use SSHExec
             end
           end
@@ -222,6 +224,7 @@ module VagrantPlugins
       autoload :ForwardPorts, action_root.join("forward_ports")
       autoload :HasSSH, action_root.join("has_ssh")
       autoload :HostMachine, action_root.join("host_machine")
+      autoload :PrepareSSH, action_root.join("prepare_ssh")
       autoload :Stop, action_root.join("stop")
       autoload :PrepareNFSValidIds, action_root.join("prepare_nfs_valid_ids")
       autoload :PrepareNFSSettings, action_root.join("prepare_nfs_settings")

plugins/providers/docker/action/prepare_ssh.rb

@@ -0,0 +1,41 @@
+module VagrantPlugins
+  module DockerProvider
+    module Action
+      class PrepareSSH
+        def initialize(app, env)
+          @app = app
+        end
+
+        def call(env)
+          # If we aren't using a host VM, then don't worry about it
+          return @app.call(env) if !env[:machine].provider.host_vm?
+
+          # Get the container's SSH info
+          info = env[:machine].ssh_info
+          info[:port] ||= 22
+
+          # Modify the SSH info to be the host VM's info
+          env[:ssh_info] = env[:machine].provider.host_vm.ssh_info
+
+          # Modify the SSH options for when we `vagrant ssh`...
+          ssh_opts = env[:ssh_opts] || {}
+
+          # Append "-t" to force a TTY allocation
+          ssh_opts[:extra_args] = Array(ssh_opts[:extra_args])
+          ssh_opts[:extra_args] << "-t"
+
+          # Append our real SSH command
+          ssh_opts[:extra_args] <<
+            "ssh -i /home/vagrant/insecure " +
+            "-p#{info[:port]} " +
+            "#{info[:username]}@#{info[:host]}"
+
+          # Set the opts
+          env[:ssh_opts] = ssh_opts
+
+          @app.call(env)
+        end
+      end
+    end
+  end
+end

plugins/providers/docker/provider.rb

@@ -123,21 +123,17 @@ module VagrantPlugins
 
       # Returns the SSH info for accessing the Container.
       def ssh_info
-        # If the Container is not created then we cannot possibly SSH into it, so
-        # we return nil.
-        return nil if state == :not_created
+        # If the container isn't running, we can't SSH into it
+        return nil if state.id != :running
 
         network = driver.inspect_container(@machine.id)['NetworkSettings']
         ip      = network['IPAddress']
 
         # If we were not able to identify the container's IP, we return nil
         # here and we let Vagrant core deal with it ;)
-        return nil unless ip
+        return nil if !ip
 
-        {
-          :host => ip,
-          :port => @machine.config.ssh.guest_port
-        }
+        { host: ip }
       end
 
       def state