[virt-tools-list] Improve behaviour with connect dialog and connection errors

[Christophe Fergeau]

Hey,

This patch series fixes various corner cases when trying to connect using
the connection dialog and when the first connection attempts fails.
Some oddities still remain in this case (for example when connecting to
a VM that asks for a SASL password and cancelling), but things are still
much more consistent.

Christophe