Explicitly set permissions on entropy files

Differential Revision:	https://reviews.freebsd.org/D3933
Submitted by:	jmg
Reviewed by:	delphij, markm
Approved by:	secteam (delphij)
MFC after:	3 days
X-MFC-to:	stable/10 stable/9

usr.sbin/bsdinstall/scripts/entropy

@@ -26,4 +26,9 @@
 #
 # $FreeBSD$
 
-dd if=/dev/random of=$BSDINSTALL_CHROOT/entropy bs=4096 count=1
+umask 077
+for i in /entropy /boot/entropy; do
+	i="$BSDINSTALL_CHROOT/$i"
+	dd if=/dev/random of="$i" bs=4096 count=1
+	chown 0:0 "$i"
+done