Fixed a critical issue in bacula::filedaemon

Previously an external file was used to determine which files/directories to
backup using the @include syntax in the FileSet resource. However, Bacula's
@include statement reads the include file from _Directors_ filesystem, not from
each FileDaemons' filesystem. This means that the $backup_files parameter of
bacula::filedaemon that populated the include file was useless, and only files
listed on Director's /etc/bacula-backup.list were backed up. Fixed this issue
and added code to get rid of the useless include files.

WARNING: this commit will temporarily render your Bacula system disfunctional
unless you first run Puppet on all of your filedaemons to update the exported
Director configuration fragments and only after that run puppet on the Director
node.

Signed-off-by: Samuli Seppänen <samuli@openvpn.net>