sanitize stdout/stderr output in blackbox test

On Windows the CR characters that were in stdout/stderr led to
very unclean output on the console and in Qt Creator.
We're removing those in the runQbs method now.

Change-Id: I4bef7bb7221bd6f656e5e7480c7a3e0e7ddb44fb
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>