power-usage-report crashes

[Kevin Fenzi]

Downstream bug: https://bugzilla.redhat.com/show_bug.cgi?id=1368376

# power-usage-report
Measurement will begin in 5 seconds. Please make sure that the
computer is idle, i. e. do not press keys, start or operate programs, and that
programs are not busy with active tasks other than the one you want to examine.
Starting measurement for 60 seconds...
Loaded 0 prior measurements
RAPL device for cpu 0
RAPL device for cpu 0
Devfreq not enabled
Preparing to take measurements
  unknown op '{'
Measurement complete. Generating report...
Traceback (most recent call last):
  File "/usr/sbin/power-usage-report", line 199, in <module>
    main()
  File "/usr/sbin/power-usage-report", line 196, in main
    powertop_report(output['powertop'])
  File "/usr/sbin/power-usage-report", line 173, in powertop_report
    while not lines[i]:
IndexError: list index out of range

Might be a missing check to see if there's a battery or not (if not, powertop doesn't generate a csv file).