How to automatically install Ansible Galaxy roles?

You should use a requirements.yml file for this use-case. Describe the roles you require, using any of a variety of install methods:

# Install a role from the Ansible Galaxy
- src: dfarrell07.opendaylight

# Install a role from GitHub
- name: opendaylight
  src: https://github.com/dfarrell07/ansible-opendaylight

# Install a role from a specific git branch
- name: opendaylight
  src: https://github.com/dfarrell07/ansible-opendaylight
  version: origin/master

# Install a role at a specific tag from GitHub
- name: opendaylight
  src: https://github.com/dfarrell07/ansible-opendaylight
  version: 1.0.0

# Install a role at a specific commit from GitHub
- name: opendaylight
  src: https://github.com/dfarrell07/ansible-opendaylight
  version: <commit hash>

Then install them:

ansible-galaxy install -r requirements.yml

Here’s a working example (installing OpenDaylight using Ansible as a Vagrant provisioner). See the relevant Ansible docs for more info.