provisioners/ansible(both): alias String-to-Symbol

String and Symbol types are different when used as a Hash key. By
default the Vagrant machine names are set in Symbol format, but users
may write their `host_vars` entries with String keys. This is a very
simple way to ensure smooth experience, without having to coerce the
data types during the config validation (e.g. with a library like
Hashie, which is currently not in the Vagrant dependencies)

See also:
- https://bugs.ruby-lang.org/issues/5964#note-17
- https://github.com/intridea/hashie#keyconversion

plugins/provisioners/ansible/provisioner/base.rb

@@ -71,7 +71,12 @@ module VagrantPlugins
         end
 
         def get_inventory_host_vars_string(machine_name)
-          vars = config.host_vars[machine_name]
+          # In Ruby, Symbol and String values are different, but
+          # Vagrant has to unify them for better user experience.
+          vars = config.host_vars[machine_name.to_sym]
+          if !vars
+            vars = config.host_vars[machine_name.to_s]
+          end
           s = nil
           if vars.is_a?(Hash)
             s = vars.each.collect{ |k, v| "#{k}=#{v}" }.join(" ")

test/unit/plugins/provisioners/ansible/provisioner_test.rb

@@ -246,6 +246,16 @@ VF
           expect(inventory_content).to match("^" + Regexp.quote(machine.name) + ".+http_port=80 maxRequestsPerChild=808")
         }
       end
+
+      it "retrieves the host variables by machine name, also in String format" do
+        config.host_vars = {
+          "machine1" => "http_port=80 maxRequestsPerChild=808"
+        }
+        expect(Vagrant::Util::Subprocess).to receive(:execute).with { |*args|
+          inventory_content = File.read(generated_inventory_file)
+          expect(inventory_content).to match("^" + Regexp.quote(machine.name) + ".+http_port=80 maxRequestsPerChild=808")
+        }
+      end
     end
 
     describe "with groups option" do