Surrounding some field names with quotes to avoid breaking CSV assumptions.

Some names can include commas, and if they're not surrounded by quotes,
then CSV parsing breaks, as was the case in
https://github.com/google/battery-historian/issues/94#issuecomment-282790498
and several other circumstances.

Test: flashed local device and ran batterystats output through Historian

Change-Id: I070c5d873d9f79996a581bf0a5f664136c0af454