tests/functional: retry when seeing ConnectionError exception

tests/functional: retry when seeing ConnectionError exception

This base class is used for many different socket connection
errors, corresponding to ECONNRESET, ECONNREFUSED, ECONNABORTED
and more. Most of these are things you might expect to see every
now and then as transient flaws. We should thus retry the asset
download when seeing them.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20250918125746.1165658-2-berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>