Backport this upstream fix for handling utf8 output from utilities run via execReadlines - https://github.com/weldr/lorax/pull/1492

This should fix intermittent problems when running lorax in other locales – output could be UTF8 and lorax was not properly parsing the exec output which could result in a crash like `ERROR livemedia-creator: 'utf-8' codec can't decode byte 0xd1 in position 4095: unexpected end of data`