When curl is given a URL of the form '<something>://' it tries to
resolve '<something>' as a host name. If the host happens to exist and
have a server then the drop might actually appear to work. Instead use
an explicit '-no-site-' host to ensure it cannot connect.
Reported-by: Gilles Khouzam <Gilles.Khouzam@microsoft.com>
Cover command invocation argument errors. Prepare infrastructure
to cover failed 'drop' cases, but do not cover them yet because
we need to collect error messages from each platform.