arch-nspawn: Force PATH to be the Arch default

systemd-nspawn use a default environ PATH value of:
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

Since filesystem 2017.08, this is no more overrided by /etc/profile
to the Arch default:
PATH=/usr/local/sbin:/usr/local/bin:/usr/bin

arch-nspawn.in

@@ -113,6 +113,7 @@ eval "$(grep '^CARCH=' "$working_dir/etc/makepkg.conf")"
 
 exec ${CARCH:+setarch "$CARCH"} systemd-nspawn -q \
 	-D "$working_dir" \
+	-E "PATH=/usr/local/sbin:/usr/local/bin:/usr/bin" \
 	--register=no --keep-unit \
 	"${mount_args[@]}" \
 	"$@"