twister: Improve handling of errors while flashing device

The patch improves handling runners errors from flashing. It
add thread termination in case of process returning non 0 exit
code. Before, even though the error was returned,
a thread was not terminated and test ended
only after timeout termination. The patch also adds information about
the failure reason to the reports

Signed-off-by: Maciej Perkowski <Maciej.Perkowski@nordicsemi.no>