on centos.  The bootstrap tty fixup needs it.

Updates based on feedback

Simplify checks for file exists

remove invalid char

Review feedback. Use regular systemd file.

Add template for docker systemd atomic

Migrate older inline= syntax to pure yml syntax for module args as to be consistant with most of the rest of the tasks
Cleanup some spacing in various files
Rename some files named yaml to yml for consistancy

- Refactor 'Check if bootstrap is needed' as ansible loop. This allows
  to add new elements easily without refactoring. Add pip to the list.
- Refactor 'Install python 2.x' task to run once if any of rc
  codes != 0. Actually, need_bootstrap is array of hashes, so map will
  allow to get single array of rc statuses. So if status is not zero it
  will be sorted and the last element will be get, converted to bool.

Closes: #961
Signed-off-by: Sergii Golovatiuk <sgolovatiuk@mirantis.com>

"shell" step doesn't support check mode, which currently leads to failures,
when Ansible is being run in check mode (because Ansible doesn't run command,
assuming that command might have effect, and no "rc" or "output" is registered).

Setting "check_mode: no" allows to run those "shell" commands in check mode
(which is safe, because those shell commands doesn't have side effects).

Closes: #961
Signed-off-by: Sergii Golovatiuk <sgolovatiuk@mirantis.com>

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>

It actually slows down things dramatically when used in combination
with Ansible.

Some systems (e.g. CentOS on Azure) have requiretty in sudoers which makes
pipelining fail.

Add tags to allow more granular tasks filtering.
Add generator script for MD formatted tags found.
Add docs for tags how-to.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>

Moved the variable setting to the apt-get install part where it matters as requested in the review.