Avoid reinstalling dependencies

[zhan9san]

With this PR, if dependencies exist, we don't need to talk to galaxy.ansible.com every time by default.

Technically, it can be done via an explicit definition as below.

dependency:
  name: galaxy
  options:
    requirements-file: requirements.yml
    force: false

Compare

If we define community.docker as a dependency,

Before

Opened /Users/jackzhang/.ansible/galaxy_token
Collection 'community.docker:3.4.8' obtained from server default https://galaxy.ansible.com/api/
Starting galaxy collection install process
Process install dependency map
Starting collection install process
Downloading https://galaxy.ansible.com/download/community-docker-3.4.8.tar.gz to /Users/jackzhang/.ansible/tmp/ansible-local-908270jolbbei/tmp8p2pq2qd/community-docker-3.4.8-ktwznndg
Installing 'community.docker:3.4.8' to '/Users/jackzhang/.ansible/collections/ansible_collections/community/docker'
community.docker:3.4.8 was installed successfully
INFO     Dependency completed successfully.
WARNING  Skipping, missing the requirements file.

After

Starting galaxy collection install process
Nothing to do. All requested collections are already installed. If you want to reinstall them, consider using `--force`.
INFO     Dependency completed successfully.
WARNING  Skipping, missing the requirements file.