ansible: silently skip unreachable hosts

Going to add this answer: a fix was added in Ansible 2.7: https://github.com/ansible/ansible/blob/stable-2.7/changelogs/CHANGELOG-v2.7.rst#major-changes

New keyword ignore_unreachable for plays and blocks. Allows ignoring tasks that fail due to unreachable hosts, and check results with is unreachable test.

EDIT: From personal experience, I need to add ignore_errors along with it for the playbook to actually continue.