* Change deprecated vagrant ansible flag 'sudo' to 'become'

* Emphasize, that the name of the pip_pyton_modules is only considered in coreos

* Remove useless unused variable

* Fix warning when jinja2 template-delimiters used in when statement

There is no need for jinja2 template-delimiters like {{ }} or {% %}
any more. They can just be omitted as described in https://github.com/ansible/ansible/issues/22397

* Fix broken link in getting-started guide

- 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>

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

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

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.