Create pbuilder base.tgz with debootstrap from stretch

buster's version doesn't work inside docker, see:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=930684

Note that apt cache is just disabled for building the base.tgz
as stretch debootstrap doesn't support it. Normal package
builds will still use apt caching.

Change-Id: I1e922833c94b19888af57a76627f11192b02f830
diff --git a/packages.mk b/packages.mk
index aa16b9b..c390d02 100644
--- a/packages.mk
+++ b/packages.mk
@@ -31,7 +31,8 @@
 		--othermirror "deb [trusted=yes] http://packages.cloud.google.com/apt mendel-day main|deb [trusted=yes] http://packages.cloud.google.com/apt mendel-bsp-$(BOARD_NAME)-day main" \
 		--distribution buster \
 		--architecture amd64 \
-		--extrapackages "crossbuild-essential-armhf crossbuild-essential-arm64 debhelper gnupg lintian"
+		--extrapackages "crossbuild-essential-armhf crossbuild-essential-arm64 debhelper gnupg lintian" \
+		--aptcache ""
 	mkdir -p $(ROOTDIR)/cache/base-tmp
 	cd $(ROOTDIR)/cache/base-tmp; \
 	sudo tar xf $@; \
diff --git a/prereqs.mk b/prereqs.mk
index 51f56f7..1b82fac 100644
--- a/prereqs.mk
+++ b/prereqs.mk
@@ -60,12 +60,18 @@
 	quilt \
 	rsync \
 	xz-utils \
+	wget \
 	zlib1g-dev
 
 prereqs:
 	sudo apt-get update
 	sudo apt-get install --no-install-recommends -y $(REQUIRED_PACKAGES)
 
+	# Hack in known-to-be-working-in-docker version, see
+	# https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=930684
+	wget -O debbootstrap.deb http://ftp.us.debian.org/debian/pool/main/d/debootstrap/debootstrap_1.0.89_all.deb
+	sudo dpkg -i debbootstrap.deb
+
 targets::
 	@echo "prereqs    - installs packages required by this Makefile"