Debugger: Work on LLDB auto-test on Linux

Write the full command to a temporary file for easier re-use.
Un-ignore the first stop, this does not seem to be needed in
the new async setup.

In some cases LLDB is not able to extract the even the top most
frame of the stopped thread (happened 2 out of 100 runs of the
QDateTime dumper). It's unclear why. For now just report the fact.

Change-Id: I76a63bc288f1ae6f5bd9b9604a47f051912b93d7
Reviewed-by: hjk <hjk@theqtcompany.com>