eloop-bench: fix reading the last write
eloop-bench: fix reading the last write

The last write was never read from the pipe in the run, so many
runs filled the kernel buffer causing an error which was not seen
because the pipe was blocking.

Set the pipes to non blocking and improve the exit conditions,
also ensuring the bench returns any error back.
While here add more timings and run critera.

Thanks to Christos Zoulas for helping.

rsmarples/dhcpcd,rsmarples/dhcpcd,rsmarples/dhcpcd