Xporter must create log file on temporary folder

Xporter must create log file on temporary folder.

Steps to reproduce the error:

1. Add attachments to an issue
2. Enable the option include attachments.
3. Go the folder <JIRA Installation Folder>/bin
4. Remove the Log.xml file
5. Remove the privileges to write on the folder /bin
6. Export the document to PDF/A
7. An error will occur and the export will be stopped.

Expected result:

1. We must create the log file on the temporary folder under the Jira home directory.