fusefs tests: quell Coverity "Argument cannot be negative" warnings

[asomers]

Summary

fusefs tests: quell Coverity "Argument cannot be negative" warnings

Must abort tests early if open(2) fails.

Coverity CID: 1432810 and many others

[cem]

I don't care about non-material Coverity findings in test code.

[asomers]

In D26635#593310, @cem wrote:

I don't care about non-material Coverity findings in test code.

Then you don't care about quality. The only way to find real bugs with tools like this is to methodically squash all the warnings.

[cem]

In D26635#593312, @asomers wrote:

Then you don't care about quality. The only way to find real bugs with tools like this is to methodically squash all the warnings.

You're incorrect on both counts, and the attitude is totally unwarranted.