This introduces two new interfaces to airshipctl:
* Bundle: represents a Kustomize rendered
collection of your documents that allows you to
iterate over or filter the documents in the bundle.
* Document: a thin wrapper around a rendered
document.
This commit also includes a proposal for a way to
represent YAML test fixtures as testdatafs.go
and a new testdata subfolder within the document
pkg.
Change-Id: I4282b27977617552c25c5ae2c3b7da44e67dd014
7eeb529053