It might print useful messages, even though they might come mixed with
other test messages.
However we can't leave stdout/stderr as is, because Coin agent hangs at
the end of the shell script, waiting for them to close. So we just
redirect them to a file.
Pick-to: 6.3 6.2
Change-Id: I797af78786b7df31131b3c3261e1c1fc00e5d460
Reviewed-by: Daniel Smith <Daniel.Smith@qt.io>