VM raises SSHPortNotDetected if ssh_info can't get the port

Also, I updated the wording on that error message a bit since it
turns out that it is possible through user error that there will
be no SSH port.

lib/vagrant/vm.rb

@@ -87,6 +87,10 @@ module Vagrant
         :forward_x11   => config.ssh.forward_x11
       }
 
+      # This can happen if no port is set and for some reason Vagrant
+      # can't detect an SSH port.
+      raise Errors::SSHPortNotDetected if !results[:port]
+
       # Determine the private key path, which is either set by the
       # configuration or uses just the built-in insecure key.
       pk_path = config.ssh.private_key_path || env.default_private_key_path

templates/locales/en.yml

@@ -109,9 +109,16 @@ en:
 
         %{key_path}
       ssh_port_not_detected: |-
-        Vagrant couldn't determine the SSH port for your VM! This is a rare,
-        exceptional event, and a bug should be filed. Please try recreating your
-        VM (vagrant destroy, then vagrant up). Sorry!
+        Vagrant couldn't determine the SSH port for your VM! Vagrant attempts to
+        automatically find a forwarded port that matches your `config.ssh.guest_port`
+        (default: 22) value and uses this for SSH. Alternatively, if `config.ssh.port`
+        is set, it will use this.
+
+        However, in this case Vagrant was unable to find a forwarded port that matches
+        the guest port and `config.ssh.port` is not set!
+
+        Please make sure that you have a forwarded port that goes to the configured
+        guest port value, or specify an explicit SSH port with `config.ssh.port`.
       ssh_unavailable: "`ssh` binary could not be found. Is an SSH client installed?"
       ssh_unavailable_windows: |-
         `vagrant ssh` isn't available on the Windows platform. The