core: more robust WIndows admin check [GH-5616]

CHANGELOG.md

@@ -52,6 +52,7 @@ BUG FIXES:
   - core: fix crash when using invalid box checksum type [GH-6327]
   - core: don't check for metadata if the download URL is not HTTP [GH-6540]
   - core: don't make custom dotfile path if there is no Vagrantfile [GH-6542]
+  - core: more robust check for admin privs on Windows [GH-5616]
   - commands/rdp: prefer `xfreerdp` if it is available on Linux [GH-6475]
   - commands/up: the `--provision-with` flag works with provisioner names [GH-5981]
   - communicator/ssh: fix potential crash case with PTY [GH-6225]

lib/vagrant/util/platform.rb

@@ -45,10 +45,13 @@ module Vagrant
           #   detect-if-running-with-administrator-privileges-under-windows-xp
           begin
             Win32::Registry::HKEY_USERS.open("S-1-5-19") {}
-            return true
           rescue Win32::Registry::Error
             return false
           end
+
+          # If we made it this far then we try a fallback approach
+          # since the above doesn't seem to be bullet proof. See GH-5616
+          (`reg query HKU\\S-1-5-19 2>&1` =~ /ERROR/).nil?
         end
 
         # This takes any path and converts it from a Windows path to a