core: error-exit machine readable output type for errors [GH-2999]

CHANGELOG.md

@@ -35,6 +35,8 @@ FEATURES:
 
 IMPROVEMENTS:
 
+  - core: Added "error-exit" type to machine-readable output which contains
+    error information that caused a non-zero exit status. [GH-2999]
   - guests/solaris: More accurate Solaris >= 11, < 11 detection. [GH-2824]
   - provisioners/chef-solo: New config `synced_folder_type` replaces the
     `nfs` option. This can be used to set the synced folders the provisioner

bin/vagrant

@@ -153,6 +153,7 @@ rescue Exception => e
   if env
     opts = { :prefix => false }
     env.ui.error e.message, opts if e.message
+    env.ui.machine("error-exit", e.class.to_s, e.message.to_s)
   else
     $stderr.puts "Vagrant failed to initialize at a very early stage:\n\n"
     $stderr.puts e.message

website/docs/source/v2/cli/machine-readable.html.md

@@ -106,6 +106,14 @@ with the machine-readable output.
 </td>
 </tr>
 
+<tr>
+<td>error-exit</td>
+<td>
+	An error occured that caused Vagrant to exit. This contains that
+	error. Contains two data elements: type of error, error message.
+</td>
+</tr>
+
 <tr>
 <td>provider-name</td>
 <td>