Update xmlsec callback logging

Update xmlsec callback logging

The main purpose of this commit is to help with debugging memory leaks in a
client app.
* Log file closing callback to make sure that files are closed eventually.
* Log only filename without the prefix in file opening callback. The prefix is
  logged elsewhere anyway. This is to avoid log truncating on some images.

Change-Id: I20bd376c18b9c2f0ab865cf9dccdaf8cedbec202