Resolve "Invalid remote dev" when tagging for autodeploy

Closes gitlab-com/gl-infra/delivery#499 (closed)

4eb89a15 - Always use canonical path for Deployer project tag

Previously the Gitlab gem was calling #to_s on the Project, which during a security release attempts to call dev_path, which doesn't exist for the Deployer project.

Now we always use its canonical path, because it only exists on Ops.

ef139448 - Add the project path to the "invalid remote" error

This makes it a bit more obvious which project raised the invalid remote error, and takes advantage of the block form of Hash#fetch to simplify the code.