Add experiment log

At the end of every run of net-eval-run, the kernel ring buffer
is read, written to a file net-eval-log in the tmp directory,
and cleared. This log of the output of dmesg may serve as a
history of the experiments performed and a debugging tool.

This log is sufficient to track what occurs during each
experiment, so many of the print statments that show the
progress of the experiments is removed.