Remove the remoteFetchTime metric.

This metric is confusing: it adds up all of the time to fetch
shuffle inputs, but fetches often happen in parallel, so
remoteFetchTime can be much longer than the task execution time.

@squito it looks like you added this metric -- do you have a use case for it?

cc @shivaram -- I know you've looked at the shuffle performance a lot so chime in here if this metric has turned out to be useful for you!

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #62 from kayousterhout/remove_fetch_variable and squashes the following commits:

43341eb [Kay Ousterhout] Remote the remoteFetchTime metric.
Added CPU logging
Added network logging
Fixed sign issues, changed to Scala files
Added logging to worker and fixed overflow
Fixed overflow issue in parsing
Added time to all log messages and removed commas for easier parsing
Add logging for task start/finish millis
Increase logging frequency
More comma removal
Check for non-zero elapsed CPU time
Check for non-zero time delta
Added new CPU utilization computation metric
Check for non-zero elapsed time
Much more extensive CPU logging
Fixed int/double division issue
Fixed typo and added idle time logging
Added parsing of diskstats file
Fixing compile errors
Fixed compile issues