Change the hashref file to include the timestamp

[halostatue]

With the release of cartage-rack 1.1, it was modified to support a two-line release_hashref of the format:

5aee3542c3c1900b12080518630c50b878b62f6a
20150411180324

We need to support that format.

[halostatue]

This is being fixed, in a different way, in Cartage 2.0. #9 adds a release-metadata.json file that contains this information and much more.