Parse errors for curtin preseeds aren't reported

[Kai Mast]

If for example /etc/maas/preseeds/curtin_userdata contains invalid syntax, it seems like the script is just ignored without reporting any error.

This is super annoying. There also seems no way to look at the output of the script in this case ( I can only do that if it runs and fails....)

[Raphaël Badin (rvb)]

Right, what MAAS could do here is at least check that the content it uses when composing the curtin preseed (in src/maasserver/preseed.py) is a valid YAML file.