kernel: config.vm.host_name works again

CHANGELOG.md

@@ -11,6 +11,7 @@ FEATURES:
 IMPROVEMENTS:
 
   - core: add `--color` to any Vagrant command to FORCE color output. [GH-2027]
+  - core: "config.vm.host_name" works again, just an alias to hostname.
   - commands/plugin/install: Post install message of a plugin will be
     shown if available. [GH-1986]
   - commands/status: cosmetic improvement to better align names and

plugins/kernel_v2/config/vm.rb

@@ -44,6 +44,12 @@ module VagrantPlugins
         @__synced_folders              = {}
       end
 
+      # This was from V1, but we just kept it here as an alias for hostname
+      # because too many people mess this up.
+      def host_name=(value)
+        @hostname = value
+      end
+
       # Custom merge method since some keys here are merged differently.
       def merge(other)
         super.tap do |result|