Added mkdir command filter for WinRM to be compatible with PS4+

plugins/communicators/winrm/command_filter.rb

@@ -11,6 +11,7 @@ module VagrantPlugins
         "test",
         "uname",
         "which",
+        "mkdir",
       ]
 
       # Filter the given Vagrant command to ensure compatibility with Windows

plugins/communicators/winrm/command_filters/mkdir.rb

@@ -0,0 +1,25 @@
+module VagrantPlugins
+  module CommunicatorWinRM
+    module CommandFilters
+      # Converts a *nix 'mkdir' command to a PowerShell equivalent
+      class Mkdir
+        def filter(command)
+          # mkdir -p /some/dir
+          # mkdir /some/dir
+          cmd_parts = command.strip.split(/\s+/)
+          dir = cmd_parts.pop
+          while !dir.nil? && dir.start_with?('-')
+            dir = cmd_parts.pop
+          end
+          # This will ignore any -p switches, which are redundant in PowerShell,
+          # and ambiguous in PowerShell 4+
+          return "mkdir #{dir} -force"
+        end
+
+        def accept?(command)
+          command.start_with?('mkdir ')
+        end
+      end
+    end
+  end
+end