Fixes #26154 - implement pxedir method for operatingsystem base

Default MediumProvider tries to use pxedir method on the operating
system to generate a unique id. Not all OSes implement these method,
causing provisioning to fail for windows.

(cherry picked from commit f905973)

app/models/operatingsystem.rb

@@ -210,6 +210,10 @@ def pxe_files(medium_provider, _arch = nil, host = nil)
     end
   end
 
+  def pxedir
+    ""
+  end
+
   def kernel(medium_provider)
     bootfile(medium_provider, :kernel)
   end

app/models/operatingsystems/rancheros.rb

@@ -13,10 +13,6 @@ def url_for_boot(file)
     PXEFILES[file]
   end
 
-  def pxedir
-    ''
-  end
-
   def display_family
     'RancherOS'
   end

app/models/operatingsystems/xenserver.rb

@@ -10,10 +10,6 @@ def pxe_type
     "xenserver"
   end
 
-  def pxedir
-    ""
-  end
-
   def xen(medium_provider)
     bootfile(medium_provider, :xen)
   end