Device support: Polish DeviceApplicationRunner.

Remove timeout check (part of DeviceProcess now), react to the
DeviceProcess' error() signal, remove unneeded members, improve
messages.
What's left is a light-weight wrapper around DeviceProcess suitable for
run controls. Removal would result in identical boiler-plate code in
several places.

Change-Id: Ib306369df8dbf72dddb8ca305d256870a121dd63
Reviewed-by: Daniel Teske <daniel.teske@digia.com>