create all users in one place

* rename 'admin_users' tasks to just 'users'
* move service account creation from 'bootstrap.yml' to the above
  mentioned task list
slightly change the way sudoers are ensured

* make sure '#includedir ...' is present
* do not use template (we do not need it atm) and use the file verbatim
* remove the corresponding part from bootstrap.yml
move notes from bootstrap.yml to docs/ansible-todo.txt

* related to the crontask
do not install python

* python2 is installed as a dependency for ansible and is taken care of
  in 'bootstrap.yml' playbook
unify package installation

* install all mandatory packages
* do not install sudo separately (though this can be kept just to be
  sure)
* install all utility packages
* remove the functionality from 'bootstrap.yml'

Fixes ticket:3036
run site.yml during bootstrap

* supply '-u root' as otherwise it will use current user