Fix 404 on actions with plugin re-installs with UPM

Issue Summary

Fix 404 on actions with plugin re-installs with UPM. It seems re-installing an app with XWork actions results in 404 in its actions on Struts

This is reproducible on Data Center: (yes) 

Steps to Reproduce

1. re-install a plugin, eg: confluence-view-storage-format plugin
2. hit http://localhost:8080/confluence/plugins/viewstorage/viewpagestorage.action?pageId=<pageid>, you shouldn't see 404.

Expected Results

No 404 on re-installed plugin actions.

Actual Results

404 on actions

Workaround

Try restarting Confluence Server after the plugin state change.