The test suite was not updated to deal with the new assumptions of the
HCL2-based expression evaluator, which requires configuration to exist
as well as state. Therefore we add a simple configuration fixture to have
it validate expressions against.
This also includes updates to expect the different error messages that the
new evaluator produces.
There are still some errors left, because our expression evaluator now
does more validation than before and so we'll need to (in a subsequent
commit) actually use a fixture configuration for these tests so that the
validations will allow the expressions to be validated.