generic/294: Filter backquotes from mknod error output

Really old versions of coreutils (mine are 8.12) quote a filename in the
output with a backquote in the beginning and normal quote in the end.
Improve _filter_mknod to handle that.

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

common/filter

@@ -389,7 +389,7 @@ _filter_od()
 # mknod errors print unquoted filenames
 _filter_mknod()
 {
-	sed -e "s/mknod: '\(.*\)': File exists/mknod: \1: File exists/"
+	sed -e "s/mknod: [\`']\(.*\)': File exists/mknod: \1: File exists/"
 }
 
 # make sure this script returns success