guests/nixos: don't detect as Windows [GH-4302]

CHANGELOG.md

@@ -19,6 +19,7 @@ IMPROVEMENTS:
 
 BUG FIXES:
 
+  - core: Windows is not detected as NixOS in some cases. [GH-4302]
   - core: Fix encoding issues with Windows. There are still some outlying
       but this fixes a few. [GH-4159]
   - commands/package: base package won't crash with exception [GH-4017]

plugins/communicators/winrm/command_filters/test.rb

@@ -8,7 +8,7 @@ module VagrantPlugins
           # test -f /tmp/afile
           # test -L /somelink
           # test -x /tmp/some.exe
-          
+
           cmd_parts = command.strip.split(/\s+/)
           flag = cmd_parts[1]
           path = cmd_parts[2]

plugins/guests/nixos/guest.rb

@@ -4,6 +4,12 @@ module VagrantPlugins
   module GuestNixos
     class Guest < Vagrant.plugin("2", :guest)
       def detect?(machine)
+        # For some reason our test passes on Windows, so just short
+        # circuit because we're not Windows.
+        if machine.config.vm.communicator == :winrm
+          return false
+        end
+
         machine.communicate.test("test -f /run/current-system/nixos-version")
       end
     end