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/docker/tasks/main.yml

@@ -12,6 +12,7 @@
       paths:
       - ../vars
       skip: true
+  tags: facts
 
 - name: check for minimum kernel version
   fail:
@@ -20,6 +21,7 @@
           {{ docker_kernel_min_version }} on
           {{ ansible_distribution }}-{{ ansible_distribution_version }}
   when: (ansible_os_family != "CoreOS") and (ansible_kernel|version_compare(docker_kernel_min_version, "<"))
+  tags: facts
 
 - name: ensure docker repository public key is installed
   action: "{{ docker_repo_key_info.pkg_key }}"
@@ -76,4 +78,4 @@
     enabled: yes
     state: started
   with_items:
-    - docker
+    - docker