test: Remove a race in check-storage.
web: Release client of the #service page.

This was an oversight.
web: Add cockpit.set_watched_client function.
web: Show modal dialog when single-server pages get disconnected.

Fixes #598
web: Don't reconnect D_Bus clients when acquired

This is not useful anymore since we now can let the user deal with it
in the "Disconnected" dialog.
web: Also use the "Disconnected" dialog on the dashboard.

This is more consistent and the modality doesn't hurt much since a
problem with localhost very likely means that no machine can be
reached.
web: Show modal dialog on containers page when disconnected.