backup: Set owner of {ex,in}clude{,.user} files to "root"

backup: Set owner of {ex,in}clude{,.user} files to "root"

Since these files are static, there is no legitimate reason why they
should be owned (hence writable) by "nobody". Also, according to
configroot's LFS file, this is the intended behaviour for the *.user
files, which is then overwritten by the backup LFS file. Therefore, set
the file mode of these statically - configroot does not feature other
files in /var/ipfire/backup/ anyway.

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>