provisioners/ansible_local: use the inventory directory

Like in the (remote) `ansible` provisioner, it is preferred to pass the
directory that contains the generated inventory file. This way, advanced
inventory usages can be achieved by adding more inventory files into the
same directory.

Related to #2103 and #6500

[ci skip]

plugins/provisioners/ansible/provisioner/guest.rb

@@ -113,7 +113,7 @@ module VagrantPlugins
             comm.upload(temp_inventory.path, inventory_path)
           end
 
-          return inventory_path
+          return inventory_basedir
         end
 
         def generate_inventory_machines