Double slashes causes inconsistency between open() and exists()

[JarrettSpiker]

If a path has double slashes (e.g. http://artifactory:8081/artifactory//something/artifact.jar) then, assuming that the artifact does actually exist, ArtifactoryPath.exists() will return True.

However, when open() is called on the same path, it will fail with RuntimeError: 404

Obviously it would make life easier if open() would succeed on such a call, but barring this exists() should fail so that it is possible to check for artifacts without actually trying to open them.