providers/docker: validate create args is list [GH-4850]

plugins/providers/docker/config.rb

@@ -231,6 +231,10 @@ module VagrantPlugins
           end
         end
 
+        if !@create_args.is_a?(Array)
+          errors << I18n.t("docker_provider.errors.config.create_args_array")
+        end
+
         @links.each do |link|
           parts = link.split(":")
           if parts.length != 2 || parts[0] == "" || parts[1] == ""

templates/locales/providers_docker.yml

@@ -123,6 +123,8 @@ en:
           "build_dir" must exist and contain a Dockerfile
         build_dir_or_image: |-
           One of "build_dir" or "image" must be set
+        create_args_array: |-
+          "create_args" must be an array
         invalid_link: |-
           Invalid link (should be 'name:alias'): "%{link}"
         invalid_vagrantfile: |-

test/unit/plugins/providers/docker/config_test.rb

@@ -90,6 +90,18 @@ describe VagrantPlugins::DockerProvider::Config do
     end
   end
 
+  describe "#create_args" do
+    before do
+      valid_defaults
+    end
+
+    it "is invalid if it isn't an array" do
+      subject.create_args = "foo"
+      subject.finalize!
+      assert_invalid
+    end
+  end
+
   describe "#expose" do
     before do
       valid_defaults