Fix RSpec 3.x syntax

* 1 conversion
    from: it { should ... }
      to: it { is_expected.to ... }

* 1 conversion
    from: its(:attr) { }
      to: describe '#attr' do subject { super().attr }; it { } end

Change-Id: I92fdb3dd3f24cbfb736ddb1b4fbb87ea1cc9f09f
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>

spec/acceptance/basic_vswitch_spec.rb

@@ -43,7 +43,10 @@ describe 'basic vswitch' do
     end
 
     describe command('ovs-vsctl show') do
-      its(:stdout) { should match /br-beaker/ }
+      describe '#stdout' do
+        subject { super().stdout }
+        it { is_expected.to match /br-beaker/ }
+      end
     end
   end
 end