clone: treat "checking connectivity" like other progress

clone: treat "checking connectivity" like other progress

When stderr does not point to a tty, we typically suppress
"we are now in this phase" progress reporting (e.g., we ask
the server not to send us "counting objects" and the like).

The new "checking connectivity" message is in the same vein,
and should be suppressed. Since clone relies on the
transport code to make the decision, we can simply sneak a
peek at the "progress" field of the transport struct. That
properly takes into account both the verbosity and progress
options we were given, as well as the result of isatty().

Note that we do not set up that progress flag for a local
clone, as we do not fetch using the transport at all. That's
acceptable here, though, because we also do not perform a
connectivity check in that case.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>