add ec2 i2.xlarge device data
print the generated filename and elapsed time
remove unneeded slicing of buckets

Last night's changes got rid of partial buckets so the additional
code is no longer needed.
drop corrupted lines in CSV files

I got a couple files with some null characters in them. For most
of these tests, it's not a big deal to drop a few samples so that's
what happens now. An error is still printed and I haven't seen it again.
Clean up record sorting & export more json.

Record sorting was causing weird results in the graphs so
now the summary is a bit safer about it and does multiple
sorts in the percentiles() function so the data is always
in time order again when it returns. This is a bit expensive
but doesn't seem to hurt runtime too badly.

Also started exporting other fields into the JSON that might
be useful in graphs.