storaged: add parser for dumpsys storaged output

Rank uids by io stats and display their tasks. Can either rank by combining
io stats for same uids or io stats for the last appearing uid.
See python ranker.py -h for details.

Test: python ranker.py -i io.txt -o output.txt -u 20 -cnt

Bug: 63739275
Change-Id: Ieee1d7a9bf190266fc6a055c0922434fcd9099c6