containers test: Wait a few more seconds for the socket to be deleted

Previously, we were waiting a few seconds for the dbus-daemon to stop listening, then trying to connect again and asserting that it failed, then immediately asserting that the socket had actually been deleted. However, there is a race here: the dbus-daemon stops listening on the socket, and then deletes it. If the test client wins the race by probing to see whether the socket is present after the dbus-daemon has stopped listening but before the dbus-daemon has deleted it, then the test will fail.

This intermittently happens on Gitlab-CI, most recently in https://gitlab.freedesktop.org/smcv/dbus/-/jobs/45694.