log_output: Format help
log_output: remove unnecessary SECONDS var write
log_output: check_env more
log_output: Faster with -M<num> without -t

"-t -M" is fastest of other arguments combination if command support
 SIGPIPE, but just "-M" is slower...
This commit turbos just "-M" with head -n<num>
log_output: fix not all log printed

if arg has '-L,-t' and command lives for longer time