Add the ability to control when `cvise_extra` directories are created.

[vext01]

I have a cvise setup where the interestingness oracle needs to copy a whole source code directory into the temp dir in order for a binary to be compiled.

cvise was filling my filesystem because it creates these cvise_extra directories when there's a timeout. And then those directories would get copied into the temp dir each time. Eventually the disk would be filled and cvise would crash in strange ways.

I've worked around this by using rsync to not copy those directories into the cvise temp dirs, like this:

rsync -a --exclude 'cvise_extra_*' ${YKLUA_HOME}/creduce/src .
cp onelua.c src/
cd ./src
make onelua
./onelua -e "_U=true" ${YKLUA_HOME}/tests/events.lua 2>&1 | grep 'trace_builder.rs:389'

But it would be nice if there was a way to disable creation of those directories upon a timeout.

[marxin]

Oh, good catch! These folders are generally created every time a potential C-Vise bug encounters, where timeouts of a C-Vise pass are commonly known as such a bug. Thus, we create reproducer folders where all intermediate files are preserved for further analysis.

But in this case (timeout) I doubt we should preserve it for further analysis. Would you like to develop a PR that will remove the creation of reproducers for situations where int. tests time out?

https://github.com/marxin/cvise/blob/16a34b273966e32843b3f193590198e2a769b1b0/cvise/utils/testing.py#L396

[vext01]

Hrm. I'm actually starting to question why cvise has a built-in timeout mechanism, when (as we discussed in #145) the timeout utility does a better job of it.

For backwards compat with creduce, I suppose.