reduce/fuzz: improve command line args (#2932)

* reduce: add -o. 
* reduce: add --temp-file-prefix. 
* reduce: add interestingness test args. 
* Detect bad args with one dash e.g. -a. 
* reduce: fix validator args. 
* Add = to args that require it. 
* More consistent naming/style across fuzz/reduce. 
* Change some 0 exit codes to 1.