Cache googleclouds zones so that populate dont have to list all each time called.

* in _rrset_for_X functions, use values instead of data attribute.
* Small typo fixes and removals of redundant steps etc.
* Unset GOOGLE_APPLICATION_CREDENTIALS in coverage script.

remove _GoogleCloudRecordSetMaker into the GoogleCloudProvider, and consolidate methods.

Also make _data_for_SPF and _data_for_TXT the same method.

This reverts commit 5a3d844559.

Proposed google cloud provider for #23

Implement "chunked" TXT/SPF value support for long values

This implements it transparently at Record level. Providers that need things to
be chunked (seems to just be Route53 an Dyn) switch to use `chunked_values`, but
everything else can stick with `values`. I've run through each provider I have
access to verifying that things operate as expected/required. OVH and Azure are
untested.

0.8.7 release

`Included` and `Excluded` can be used to filter records for one or more specific provider(s). This can be extremely useful when certain record types are not supported by a provider and you want only that provider to receive an alternative record.

See also: https://github.com/github/octodns/issues/26

Add OVH as octodns provider

Add an octoDNS provider for rackspace.

Cut v0.8.6

Fixes for cloudflare CAA support

CAA support

Seem to be pretty inconsistently implemented/validated across providers so
just shrug and move on.

Add support for increasing Route53 retries

Fixed TXT record bug when creating the record with Azure

Allow proto to be specified for powerdns

This allows a scheme to be set for the PowerDNS API. It defaults to
http to retain backwards compatibility.