Add data serialization time to waterfall
Fixed bugs in straggler computation.

This commit fixes two bugs: first, the log output incorrectly
characterized the improvement from removing stragglers; and
second, the method to compute the speedup from eliminating the slowest
5% of tasks was incorrect because it compared the task.runtime METHOD
(rather than the actual value) to a threshold -- so the comparision
was invalid.
Improved straggler handling code.

Adds more diagnosis of why stragglers occur.
Added file to diagnose stragglers for one job.
Fixed bug in straggler/non-straggler time comparison.
Changed straggler metrics to use progress rate rather than runtime.
Added parsing of locality as well as a test.
Added code to count how many HDFS read stragglers are non-local
Added file to parse stats about each query.
Refactored get_query_stats to output more info.
Add job logs for big data benchmark runs.
Add script to create disk breakdown CDFs
Fixes to disk time logging
Added output write time, new file to compute ideal runtime.
Added estimated serialization/deserialiation time
Add speedup from eliminating output write