Add script log-f3wr

This script runs f3write and f3read, echos their output to
the terminal, and records their output into a log file.
f3write: account for option --end-at

This patch improves the progress percentage and estimate of
time to finish when option --end-at requires f3write to write
less than the amount of free space available.
Merge remote-tracking branch 'upstream/master' into freebsd_patch

Conflicts:
	log-f3wr