Tighten output check in Cucumber step testing RSpec success

This change ensures no errors were reported, and that both checks are
performed before reporting any failures.

lib/aruba/cucumber/testing_frameworks.rb

@@ -52,8 +52,11 @@
 
 # RSpec
 Then(/^the spec(?:s)? should all pass$/) do
-  step 'the output should contain "0 failures"'
-  step 'the exit status should be 0'
+  aggregate_failures do
+    expect(last_command_stopped)
+      .to have_output an_output_string_matching('examples?, 0 failures')
+    expect(last_command_stopped).to have_exit_status 0
+  end
 end
 
 # RSpec