Add test for Apertis update manager error conditions

Add test to check proper behavior in the following circumstances:

• Power cut during an update
• USB mass storage unplug during an update
• The disk is full during an update

Signed-off-by: Denis Pynkin denis.pynkin@collabora.com Signed-off-by: Frédéric Dalleau frederic.dalleau@collabora.com