Don't save entropy inside jails.

As of r126744, we no longer feed the entropy device in jails upon
start, and collecting them is no longer useful.

PR:		conf/126744
Submitted by:	Eugene Grosbein <eugen grosbein net> (with minor changes)
MFC after:	1 week
Approved by:	so (des)

libexec/save-entropy/save-entropy.sh

@@ -42,6 +42,8 @@ elif [ -r /etc/rc.conf ]; then
 	. /etc/rc.conf 2>/dev/null
 fi
 
+[ $(/sbin/sysctl -n security.jail.jailed) = 0 ] || exit 0
+
 case ${entropy_dir} in
 [Nn][Oo])
 	exit 0