CI: dump_machine_logs.sh, show more info on errors when failing to connect to miniserve
Sometimes we have failure to get node logs with dump_machine_logs.sh, but we don't know what kind of error exactly and we can't easily distuinguish between "the node isn't reachable at all", "miniserve isn't running, port does not answer" and "miniserve crashes when giving us the dump".
With this MR I hope we'll see more.
(This MR also simplifies how we retry connections.)
Edited by Thomas Morin