Eliminate prints to stderr for normal messages, because it leads to exceptional
returns in TCL-scripts e.g. when run-script is triggered by the autopilot even
if the script's return code itself will be zero.
When invoking the bootstrap build in the L4RE build-system to create
a single elf-image containing all needed files to boot a scenario, don't
use the 'ENTRY' variable, but 'E' variable instead. Otherwise 'ENTRY'
might get overridden (dependent on the make-version). Moreover, using
'E' seems to be the way L4Re is expecting it has to be invoked.
Fixes#226
