runme: rewrite ubuntu / debian rootfs generation logic

Mainly remove use of buildroot as initial rootfs for use by QEMU.
Instead the generated device kernel can be used

For initial rootfs - Ubuntu has a downloadable minimal rootfs, Debian
can boot result of debootstrap stage 1.

docker/Dockerfile

@@ -14,7 +14,7 @@ RUN set -e; \
 	apt-get -y upgrade; \
 	:
 
-RUN apt-get update ; apt-get -y install acpica-tools bc bison build-essential cpio device-tree-compiler dosfstools e2tools flex fuseext2 g++ gcc git kmod libssl-dev make meson mtools multistrap ninja-build p7zip p7zip-full pandoc parted python python2 python3 qemu-system-arm rsync squashfs-tools sudo tar u-boot-tools unzip wget xz-utils
+RUN apt-get update ; apt-get -y install --no-install-recommends acpica-tools bc bison build-essential ca-certificates cpio debian-archive-keyring debootstrap device-tree-compiler dosfstools e2tools fakeroot flex fuseext2 g++ gcc git kmod libssl-dev make meson mtools multistrap ninja-build p7zip p7zip-full pandoc parted python python2 python3 qemu-system-arm rsync squashfs-tools sudo tar u-boot-tools unzip wget xz-utils
 
 # build environment
 WORKDIR /work

docker/entry.sh

@@ -35,8 +35,6 @@ sudo -u $user git config --global user.email "support@solid-run.com"
 cd /work
 # now run the build script as the build user, preserving config variables
 sudo \
-	--preserve-env=RELEASE,DDR_SPEED,SERDES,UEFI_RELEASE \
-	--preserve-env=SHALLOW,SECURE,ATF_DEBUG,DISTRO \
-	--preserve-env=BR2_PRIMARY_SITE \
+	--preserve-env=APTPROXY,ATF_DEBUG,DDR_SPEED,DEBIAN_ROOTFS_SIZE,DEBIAN_VERSION,DISTRO,MC_RELEASE,RELEASE,SECURE,SERDES,SHALLOW,UBUNTU_ROOTFS_SIZE,UBUNTU_VERSION,UEFI_RELEASE \
 	-u $user \
 	./runme.sh