add switch for install bundler

[vkill]

Hi

I add a switch for install bundler, because we cannot install any gem by normal way in China.

After this modification, I can install bundler and some gems like this

---
- hosts: server
  roles:
    - ansible-role-ruby
      ruby_install_from_source: True
      ruby_version: 2.2.2
      ruby_download_url: http://cache.ruby-lang.org/pub/ruby/ruby-2.2.2.tar.gz
      ruby_install_bundler: False
      ruby_install_gems: []

  tasks:
    - name: 'Replace gem source for user'
      shell: gem sources --add https://gems.ruby-china.org/ --remove https://rubygems.org/
      become: yes
      become_user: "{{ ansible_ssh_user }}"

    - name: 'Replace gem source for root'
      shell: gem sources --add https://gems.ruby-china.org/ --remove https://rubygems.org/
      become: yes
      become_user: "root"

    - name: Install Bundler.
      gem: name=bundler state=present user_install=no

    - name: Install configured gems.
      gem: "name={{ item }} state=present"
      become: yes
      become_user: "{{ ansible_ssh_user }}"
      with_items:
        - pry

Please review it, thanks.

[geerlingguy]

Sounds good, thanks!