In dry-run mode, treat SUBIQUITY_DEBUG as a comma-separated list of
things to fail:
* install-fail: curtin install fails
* copy-logs-fail: the postinstall copying of logs fails
* bpfail-full: full block device probing fails
* bpfail-restricted: restricted block device probing fails
In addition, control-u makes the UI crash in dry-run mode.
(This is all for testing of crash report generation but does not depend
on that).