* Refactor tests out of module for certbot-dns-cloudflare
* Refactor tests out of module for certbot-dns-cloudxns
* Refactor tests out of module for certbot-dns-digitalocean
* Refactor tests out of module for certbot-dns-dnsimple
* Refactor tests out of module for certbot-dns-dnsmadeeasy
* Refactor tests out of module for certbot-dns-gehirn
* Refactor tests out of module for certbot-dns-google
* Refactor tests out of module for certbot-dns-linode
* Refactor tests out of module for certbot-dns-luadns
* Refactor tests out of module for certbot-dns-nsone
* Refactor tests out of module for certbot-dns-ovh
* Refactor tests out of module for certbot-dns-rfc2136
* Refactor tests out of module for certbot-dns-sakuracloud
* Refactor tests out of module for certbot-dns-route53
* Move certbot-dns-google testdata/ under tests/
* Use pytest for dns plugins
* Exclude pycache and .py[cod]
* Added DNS based authenticator plugin for Linode
* Added linode plugin to docs
* Added Dockerfile
* Added .gitignore and readthedocs.org.requirements.txt
* Updated default_propagation_seconds
* Updated according to changes requested
* Bump version to 0.26.0
* Advertise our packages work on Python 3.7.
