CLOUDFLARE: Integration tests should use API Token, not user/key (#557)
CLOUDFLARE: Integration tests should use API Token, not user/key (#557)

* providers/cloudflare: Support API tokens

Cloudflare API tokens are a new way to authenticate to Cloudflare API.
Unlike the Global API key, tokens can be given specific permissions to
only access parts of the API. See [1] for details.

[1] https://blog.cloudflare.com/api-tokens-general-availability/

This commit introduces a new credential for cloudflare called
`apitoken`, which is mutually exclusive with `apiuser` and `apikey`.

In order for DNSControl to work with this token, it should have the
right to read DNS zones and edit DNS records.

Closes #534

* CLOUDFLARE: Update integration tests for api token

StackExchange/dnscontrol,StackExchange/dnscontrol,StackExchange/dnscontrol