* Remove leftover files for Coreos

Coreos was replaced by flatcar in 058438a2 but the file was copied
instead of moved.

* Remove workarounds for resolved ansible issues

* boostrap: Use first_found to include per distro

Using directly ID and VARIANT_ID with first_found allow for less manual
includes.
Distro "families" are simply handled by symlinks.

* boostrap: don't set ansible_python_interpreter

- Allows users to override the chosen python_interpreter with group_vars
  easily (group_vars have lesser precedence than facts)
- Allows us to use vars at the task scope to use a virtual env

Ansible python discovery has improved, so those workarounds should not
be necessary anymore.
Special workaround for Flatcar, due to upstream ansible not willing to
support it.

* Add README to bootstrap-os role

* Rework bootstrap-os once more

* Document workarounds for bugs/deficiencies in Ansible modules
* Unify and document role variables
* Remove installation of additional packages and repositories
* Merge Ubuntu and Debian tasks
* Remove pipelining setting from default playbooks
* Fix OpenSUSE not running its required tasks

The docker service provided by the containers-basic bundle is masked
in ClearLinux distribution. This is causing errors in the following
steps. This commit ensures that the unit is not masked.

* bootstrap: rework role

* support being called from a non-root user
* run some commands in check mode
* unify spelling/task names

* bootstrap: fix wording of comments for check_mode: false

* bootstrap: remove setup-pipelining task

Signed-off-by: Ganesh Maharaj Mahalingam <ganesh.mahalingam@intel.com>