Add tags

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>

roles/bootstrap-os/tasks/bootstrap-ubuntu.yml

@@ -5,6 +5,7 @@
   raw: which python
   register: need_bootstrap
   ignore_errors: True
+  tags: facts
 
 - name: Bootstrap | Install python 2.x
   raw: apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y python-minimal
@@ -12,3 +13,4 @@
 
 - set_fact:
     ansible_python_interpreter: "/usr/bin/python"
+  tags: facts