unhandled exception when running cpufreq_test.py as a non-root user

Forgot to use sudo to run cpufreq_test.py manually and instead of a useful message I got a traceback:

$ /usr/lib/plainbox-provider-checkbox/bin/cpufreq_test.py -d |tee -a /home/bladernr/cpufreq.log
---------------------
| CpuFreqTest Begin |
---------------------
* disabling thread siblings (hyperthreading):
  - disabling cores: {4, 5, 6, 7}
Unable to write file: /sys/devices/system/cpu/cpu4/online
ERROR: Unable to write file: /sys/devices/system/cpu/cpu4/online
Traceback (most recent call last):
  File "/usr/lib/plainbox-provider-checkbox/bin/cpufreq_test.py", line 162, in _write_sysfs
    with open(abs_path, 'wb') as _file:
PermissionError: [Errno 13] Permission denied: '/sys/devices/system/cpu/cpu4/online'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/plainbox-provider-checkbox/bin/cpufreq_test.py", line 765, in <module>
    sys.exit(main())
  File "/usr/lib/plainbox-provider-checkbox/bin/cpufreq_test.py", line 761, in main
    return cpu_freq_test.execute_test()
  File "/usr/lib/plainbox-provider-checkbox/bin/cpufreq_test.py", line 360, in execute_test
    self.disable_thread_siblings()
  File "/usr/lib/plainbox-provider-checkbox/bin/cpufreq_test.py", line 250, in disable_thread_siblings
    self._write_sysfs(fpath, 0)
  File "/usr/lib/plainbox-provider-checkbox/bin/cpufreq_test.py", line 166, in _write_sysfs
    'Unable to write file: %s' % abs_path)
__main__.CpuFreqTestError

This exception should be handled (and realistically, should never be hit, the script should immeidately exit if the user is not root/sudo)