netops: make the path optional in URLs
When we're dealing with proxy addresses, we only want a hostname and
port, and the user would not provide a path, so make it optional so we
can use this same function to parse git as well as proxy URLs.
netops: error out on url without a path
In order to connect to a remote server, we need to provide a path to the
repository we're interested in. Consider the lack of path in the url an
error.