Fix depends

The only relevant commit is 4c0d4bd4, the other commits are trivial.

This commit reinstate hashicorp-go-plugin-dev as a dependency, even though we use a vendor copy to build (vendoring has higher priority during the go build, that's why we can have both the go package from Debian and from vendor). This is explained more in details in the commit message.

The dependency hashicorp-go-plugin-dev was removed by me. I noticed that it was a mistake while working on consul.

Please review and upload, I'm waiting for this fix so that I can upload an update of consul.

Thx!