Add a base Alpine package that includes a package mirror

This means that we limit to one place where we use network access
in building, and in future all other package builds can be deterministic.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

tools/alpine/packages

@@ -0,0 +1,58 @@
+argp-standalone
+automake
+bash
+bc
+binutils
+binutils-dev
+bison
+bsd-compat-headers
+btrfs-progs
+btrfs-progs-dev
+build-base
+ca-certificates
+cdrkit
+cmake
+curl
+dhcpcd
+dosfstools
+e2fsprogs
+e2fsprogs-extra
+flex
+gcc
+git
+gmp-dev
+gummiboot
+installkernel
+iptables
+jq
+kmod
+libarchive-tools
+libc-dev
+libelf-dev
+libseccomp-dev
+linux-headers
+make
+mtools
+musl-dev
+ncurses-dev
+openntpd
+openrc
+openssh-server
+patch
+qemu-aarch64
+qemu-arm
+qemu-img
+qemu-ppc64le
+qemu-system-arm
+qemu-system-x86_64
+sed
+sfdisk
+squashfs-tools
+syslinux
+tar
+util-linux
+util-linux-dev
+vim
+xfsprogs
+xorriso
+xz