Show magically timed progress when running a shell command without a
progress parser. The assumption is that the timeout is much larger than
the expected runtime, but still an indicator for how long it might take.
Progress manager does its magic on top of that.

This is e.g. used for the update info plugin, for which checking for
updates might take quite some while.

Change-Id: Ib3d3d37b86fac17816fe592e39e26a3d484bba26
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>