Fuzzer: Emit absolute paths in commands

[kripken]

Any filename that shows up in a command that we log for the user should be an absolute path, so that the user can just copy and paste the command. Otherwise, the fuzzer runs in out/test/ which the user has to constantly type.

I looked for a better/general way to do this, but can't find anything good other than manually annotating all the relevant places...

[tlively]

:tada:

It would be great to fix this in check.py as well.