CA-122270: Support for specific xenserver.conf file

Patch this file instead of main one if present.
This file was added to avoid overriding main rsyslog.conf file.

Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>
Merge pull request #1617 from freddy77/xenserver_conf

CA-122270: Support for specific xenserver.conf file