util: add utility method to check for bad ssh urls (SEC) Our use of SSH has an exploit that will parse the first part of an url blindly as a hostname. Prior to this set of security patches, a url with '-oProxyCommand' could run arbitrary code on a user's machine. In addition, at least on Windows, a pipe '|' can be abused to execute arbitrary commands in a similar fashion. We defend against this by checking ssh:// URLs and looking for a hostname that starts with a - or contains a |. When this happens, let's throw a big abort into the user's face so that they can inspect what's going on.