persist /etc/rancher/node across reboots

Fixes #289

 k3s: v1.0.0

k3s: v1.0.0-rc6

k3s: v1.0.0-rc5

kernel: 4.15.0-70.79

Fixes #278

ccapply: add label with the value of k3os.mode

If the `k3os.mode` (read from /var/run/k3os/mode) is not empty then add
node-label `k3os.io/mode=${k3os.mode}`.

rootfs: move k3s symlinks out of overlay

Removes k3s symlink and sub-command/reexec symlinks to it from `overlay/sbin`.
These symlinks are now all declared in the rootfs Dockerfile.

This should fix and issue with wranger generation code failing on the symlinks pointing to nowhere on module copy.

Fix type-o and structure

add ctr symlink (bundled as k3s sub-command) to /usr/sbin

- live cd boot
  `./scripts/run-qemu k3os.mode=live`

- silent install
  `DISK_NAME=test.img ./scripts/run-qemu k3os.password=rancher k3os.mode=install k3os.install.silent k3os.install.device=/dev/vda`

- run installed vm
  `DISK_NAME=test.img ./scripts/run-qemu k3os.password=rancher`

- recover installed vm
  `DISK_NAME=test.img ./scripts/run-qemu k3os.password=rancher k3os.mode=live`

Adding packer templates for vSphere

k3s: v0.10.2

ssh.SetAuthorizedKeys() will now retry up to 10 times, sleeping 1 second in between,
to read public keys from github (if any are specified). This moots the need for the
ping-test in net-online and addresses #224 while maintaining a best-effort attempt to
read github public keys.

base: install mdadm

FIX: couple of typos ; moving flavor to env variable

Bump up minimum memory: live=2GB, local 1GB

- modified README
- modified Qemu scripts

* latest k3s 0.10.0

* Working example of OpenStack image with packer for k3os on aarch64

build: .dockerignore vagrant cruft

* bump versions to 0.5.0 for packer and readme

* update checksum for iso in vagrant packer builder

kernel: 4.15.0-66.75