Currently, if a command run by the exec command returns an error
code, its stdout and stderr are not saved. It could be beneficial to
store at least the stderr if requested. Additionally, avoid creating
output files when there is no content and also store the stderr
of the failed command to diag.log.
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>
88c099d756