verify-sof-firmware-load: fix dmesg.txt collection + better logs + fix -help#873

marc-hb merged 2 commits into

thesofproject:mainthesofproject/sof-test:mainfrom

marc-hb:fix-empty-dmesg-in-verify-loadmarc-hb/sof-test:fix-empty-dmesg-in-verify-loadCopy head branch name to clipboard