Screen blanking breaks some tests in Jessie

E.g. the ‘I update APT using Synaptic’ step can result in a >5 minute wait without mouse/keyboard interaction => screen blanking kicks in and no further Sikuli screen scanning is possible so the ‘Installing packages through APT’ scenario fails.

Feature Branch: feature/jessie

Parent Task: #7563 (closed)

Original created by @anonym on 10403 (Redmine)

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