Any file or directory created inside plugin folder is loaded as an app

Issue Summary

Noticed after creating any file or directory under installed-plugins folder, they are loaded as an app/plugin

Steps to Reproduce

• Create the following files and directory under installed-plugins folder
  • A backup in .zip format  (ex: installed-plugins.zip)
  • A regular txt file "text1.txt" 
  • A directory Dir1 
• Restart Jira Services 

Expected Results

• Installed-plugins.zip, text1.txt, and Dir1 shouldn't treated as a plugin and they shouldn't be listed on the installed plugin page. 

Actual Results

• Installed-plugins.zip, text1.txt, and Dir1 loaded as plugins/apps