Do a version check of xorriso and fail early if it doesn't meet the required version - https://github.com/directhex/steamos-installer/issues/18
Should exit 1 on failure
Use dpkg --compare-versions which works much better than awk for this sort of check
Use reqxorrisover in failure output as well in case it's bumped for whatever reason in the future
Merge pull request #26 from ecliptik/xorrisochk

Do a version check of xorriso