Return exit status of 1 on invalid command

Makes "vagrant destroyjj" and similar return an exit code of 1, so that
"vagrant destroyjj && vagrant up" works as expected.

lib/vagrant/cli.rb

@@ -38,7 +38,7 @@ module Vagrant
 
       if !command_class || !@sub_command
         help
-        return 0
+        return 1
       end
       @logger.debug("Invoking command class: #{command_class} #{@sub_args.inspect}")
 

test/unit/vagrant/plugin/v1/cli_test.rb

@@ -0,0 +1,31 @@
+describe Vagrant::CLI do
+
+  describe "parsing options" do
+    let(:klass) do
+      Class.new(described_class)
+    end
+
+    let(:environment) do
+      ui = double("UI::Silent")
+      ui.stub(:info => "bar")
+      env = double("Vagrant::Environment")
+      env.stub(:ui => ui)
+      env.stub(:root_path => "foo")
+      env.stub(:machine_names => [])
+      env
+    end
+
+    it "returns a non-zero exit status if an invalid command is given" do
+      result = klass.new(["destroypp"], environment).execute
+      result.should_not == 0
+    end
+
+    it "returns an exit status of zero if a valid command is given" do
+      result = klass.new(["destroy"], environment).execute
+      result.should == 0
+    end
+
+  end
+    
+end
+