emit a progress bar when parsing collectl data; it takes a while
don't bother parsing regions of collectl data that weren't part of the run
different nodes might have different hardware configurations
more idiomatic way of calculating deltas, and probably faster, too
assume bcbio log timestamps are in UTC

this will present a problem if aws instances aren't in UTC, but timeslicing
and probably other time calculations would have been implicitly broken
before this, anyway