a6cc6cd878
`docker build` accepts remote repositories using either the `git://` notation, or `git@`. Docker attempted to parse both as an URL, however, `git@` is not an URL, but an argument to `git clone`. Go 1.7 silently ignored this, and managed to extract the needed information from these remotes, however, Go 1.8 does a more strict validation, and invalidated these. This patch adds a different path for `git@` remotes, to prevent them from being handled as URL (and invalidated). A test is also added, because there were no tests for handling of `git@` remotes. Signed-off-by: Sebastiaan van Stijn <github@gone.nl>