[jjo] add DIND support to contrib/ (#3468)

* [jjo] add DIND support to contrib/

- add contrib/dind with ansible playbook to
  create "node" containers, and setup them to mimic
  host nodes as much as possible (using Ubuntu images),
  see contrib/dind/README.md

- nodes' /etc/hosts editing via `blockinfile` and
  `lineinfile` need `unsafe_writes: yes` because /etc/hosts
  are mounted by docker, and thus can't be handled atomically
  (modify copy + rename)

* dind-host role: set node container hostname on creation

* add "Resulting deployment" section with some CLI outputs

* typo

* selectable node_distro: debian, ubuntu

* some fixes for node_distro: ubuntu

* cpu optimization: add early `pkill -STOP agetty`

* typo

* add centos dind support ;)

* add kubespray-dind.yaml, support fedora

- add kubespray-dind.yaml (former custom.yaml at README.md)
- rework README.md as per above
- use some YAML power to share distros' commonality
- add fedora support

* create unique /etc/machine-id and other updates

- create unique /etc/machine-id in each docker node,
  used as seed for e.g. weave mac addresses

- with above, now netchecker 100% passes WoHooOO!
    

- updated README.md output from (1.12.1, verified
  netcheck)

* minor typos

* fix centos node creation, needs earlier udevadm removal to avoid flaky facts, also verified netcheck Ok \o/

* add Q&D test-distros.sh, back to manual /etc/machine-id hack

* run-test-distros.sh cosmetics and minor fixes

* run-test-distros.sh: $rc fix and minor formatting changes

* run-test-distros.sh output cosmetics