providers/virtualbox: validate missing keys [GH-2831]

CHANGELOG.md

@@ -66,6 +66,7 @@ BUG FIXES:
     works properly. [GH-2751]
   - providers/virtualbox: Make more internal interactions with VBoxManage
     retryable to avoid spurious VirtualBox errors. [GH-2831]
+  - providers/virtualbox: Config validation catches invalid keys. [GH-2843]
   - provisioners/chef: When chowning folders, don't follow symlinks.
   - provisioners/salt: Options can now set install type and install args.
     [GH-2766]

plugins/providers/virtualbox/config.rb

@@ -110,7 +110,7 @@ module VagrantPlugins
       end
 
       def validate(machine)
-        errors = []
+        errors = _detected_errors
 
         valid_events = ["pre-import", "pre-boot", "post-boot"]
         @customizations.each do |event, _|