Added skip_ansible_lint to avoid specific tasks

This patch makes ansible-lint not checking tasks with tag
"skip_ansible_lint".

For example,

- name: Modify permissions
  command: >
    chdir={{rt_top_dir}}
    chmod -R g-w .
  tags:
    - skip_ansible_lint
  sudo: yes
Merge pull request #40 from yosshy/for-upstream

Added skip_ansible_lint to avoid specific tasks