Two concurent docker jobs can't fetch the same cache, see
https://gitlab.com/gitlab-org/gitlab-runner/issues/1151

Closes #63

Related: #63

See #60 for details.
For Ci droplets we use LE staging CA, so we need to provide curl
with the CA cert. Surprisingly, curl will still validate certs from
LE production CA even if "--cacert=./letsencrypt_fakelerootx1.pem" is
used.

See #53

Closes #52

On CI we still prefer to use alpine system packages
since this is much faster than installing every python
package via pip.

Closes: #51

We now have the "timer" ansible callback which brings own timestamps.

Closes: #42

Also:

- Add a .talismanrc file to ignore files beeing scanned by
  Talisman, a "tool that installs a hook to your repository
  to ensure that potential secrets or sensitive information
  do not leave the developer's workstation".
  See https://thoughtworks.github.io/talisman/
- Add .gitlab-ci.yml to build image from CI

We now have:

  usage: ci-bootstrap.py [-h] (--create_droplet | --droplet_id ID) [--terminate]
                         [--verbose]

  Run bootstrap scriptto deploy Openappstack to a given node.

  optional arguments:
    -h, --help        show this help message and exit
    --create_droplet  Create droplet automatically
    --droplet_id ID   ID of droplet to deploy to
    --terminate       Terminate droplet after deploy
    --verbose         Be more verbose