node_validate should check for unknown attributes

[jschlyter]

Only the following attributes may be declared for a node:

• environment
• classes
• parameters

If any other attribute appears, node_validate should fail.

[Millnert]

Shouldn't also the program exit with non-zero return code if node_validate fails?

[jschlyter]

if node_validate fails, you get a fancy Exception - doesn't that render a non-zero exit? Or should we catch it if we can?