Anyone running (vndr) currently ends up with failing tests in OCI schema
validation because gojsonschema has fixed its "$ref" interpretation, exposing
inconsistent URI usage inside image-spec/schema.
So, this runs (vndr), and uses mtrmac/image-spec:id-based-loader
( https://github.com/opencontainers/image-spec/pull/739 ) to make the tests pass
again. As soon as that PR is merged we should revert to using the upstream
image-spec repo again.
Primarily vendor after merging mtrmac/image:openpgp.
Then update for the SigningMechanism API change.
Also skip signing tests if the GPG mechanism does not support signing.
Also abort some of the tests early instead of trying to use invalid (or
nil) values.
The current master of image-tools does not build with Go 1.6, so keep
using an older release.
Also requires adding a few more dependencies of our updated
dependencies.
