sevctl export: unable to create output file

[wainersm]

sevclt export doesn't create the cerficate file if basedir doesn't exist:

$ sudo ./sevctl export --full /opt/sev/cert_chain.cert
error: unable to create output file

It works if I create /opt/sev beforehand.

Even if it works as designed, I think the error message could be clear.

[wainersm]

ah, built from source (commit 16a2435)

[crobinso]

My PR here improves global error reporting slightly, so the underlying API error isn't hidden. It's not the most useful in this case though:

Error: unable to create output file

Caused by:
    No such file or directory (os error 2)

I don't think we should try to create the parent directory, that's not typical for cli tools in my experience. But we could add the filename to the first error message easy enough