mkarchiso: prevent interference from xorriso startup files

Options set in xorriso startup files (~/.xorrisorc) could interfere with the xorriso command run by mkarchiso.
For example, if ~root/.xorrisorc contains -dummy on, then the ISO file will be empty.

Pass -no_rc as the first option to xorriso to prevent interference and unintended behavior.

Fixes #153.