core: test file writes for home dir perms

Creating directories for some reason was allowed in Windows, but writes
would fail later.

CHANGELOG.md

@@ -53,6 +53,8 @@ BUG FIXES:
     syntax errors.
   - core: Plugins that fork within certain actions will no longer hang
     indefinitely. [GH-2756]
+  - core: Windows checks home directory permissions more correctly to
+    warn of potential issues.
   - commands/box: Box add `--force` works with `--provider` flag. [GH-2757]
   - commands/plugin: Plugin installation will fail if dependencies conflict,
     rather than at runtime.

lib/vagrant/environment.rb

@@ -621,6 +621,17 @@ module Vagrant
         end
       end
 
+      # Attempt to write into the home directory to verify we can
+      begin
+        path = @home_path.join("perm_test")
+        path.open("w") do |f|
+          f.write("hello")
+        end
+        path.unlink
+      rescue Errno::EACCES
+        raise Errors::HomeDirectoryNotAccessible, home_path: @home_path.to_s
+      end
+
       # Create the version file to mark the version of the home directory
       # we're using.
       version_file = @home_path.join("setup_version")