Distinguish between failed reductions and parse timeouts in gfauto

[afd]

The GraphicsFuzz parser can be slow on large shaders. Right now when a shader times out during parsing as part of a reduction, the reduction is shown as having failed with an exception. It would be better to single out this case and indicate why the reduction failed.

[afd]

Changing this to a gfauto issue as that's how we prefer to run fuzzing.