docs/cookbook/container: don't delete *.out and *.code during build.

If mkdocs is running in parallel, it can get upset if one of these
files exists when it lists the directory, but doesn't exist when it
goes to generate the output.  Fundamentally this is a problem in mkdocs
more than in our code, but we might as well avoid it.

docs/cookbook/container/default.runkvm.do

@@ -1,7 +1,7 @@
 ./need.sh python kvm busybox
 
 redo-ifchange "$2.initrd" memcalc.py
-rm -f "$3.out" "$3.code"
+rm -f "$1.out" "$1.code"
 
 # Linux only allows an initrd of size < 50% of RAM,
 # so set a RAM amount based on the initrd size.
@@ -16,18 +16,17 @@ kvm \
 	-no-reboot \
 	-display none \
 	-chardev stdio,mux=on,id=char0 \
-	-chardev file,id=char1,path="$3.out" \
-	-chardev file,id=char2,path="$3.code" \
+	-chardev file,id=char1,path="$1.out" \
+	-chardev file,id=char2,path="$1.code" \
 	-serial chardev:char0 \
 	-serial chardev:char1 \
 	-serial chardev:char2 >&2
-read rv <$3.code || true
+read rv <$1.code || true
 [ -z "$rv" ] && exit 99
 if [ "$rv" -eq 0 ]; then
-	sed -e 's/\r//g' "$3.out" >$3
+	sed -e 's/\r//g' "$1.out" >$3
 	echo "ok." >&2
 else
 	echo "kvm program returned error: $rv" >&2
 fi
-rm -f "$3.out" "$3.code"
 exit "$rv"