Ansibleize control script

Closes #21

See merge request openappstack/bootstrap!20

Fixes first task in
https://code.greenhost.net/openappstack/bootstrap/issues/21#note_44648

Closes #21

The reason is that we want to reduce code duplication, and use
the oas_control script from ansible, so we don't need to call docker
explicitly as before.
Shell aliases can't be used by ansible conveniently.

Upgrade to rancher to 1.6.26

Closes #37

See merge request openappstack/bootstrap!21

This includes the following version upgrades:

- Docker 18.06.1~ce~3-0~ubuntu -> 5:18.09.2~3-0~ubuntu-bionic
  Fixes CVE-2019-5736
  (http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-5736)
- rke 0.1.15 -> 0.1.16

Closes: #37

Use logging module in ci-bootstrap.py

Closes #34

See merge request openappstack/bootstrap!19

Closes #34

Upgrade to rancher to 1.6.26

Closes #33

See merge request openappstack/bootstrap!18

This includes the following version upgrades:

- Kubernetes v1.12.3 -> v1.12.5
- rke 0.1.14 -> 0.1.15

[Rancher 1.6.26 supports Docker 18.09](https://github.com/rancher/rancher/releases/tag/v1.6.26),
but rke 0.1.14 stil doesn't, see
https://code.greenhost.net/openappstack/bootstrap/issues/33#note_44119.

Closes: #33

Improve CI further

See merge request openappstack/bootstrap!15

RKE logging

Closes #20

See merge request openappstack/bootstrap!13