Fix theme update test

Author: schlessera

features/theme.feature

@@ -676,6 +676,8 @@ Feature: Manage WordPress themes
 
   Scenario: Excluding a missing theme should not throw an error
     Given a WP install
+    And I run `wp theme delete --all --force`
+    And I run `wp theme install p2 --version=1.5.5 --activate`
     And I run `wp theme update --all --exclude=missing-theme`
     Then STDERR should be empty
     And STDOUT should contain: