crypt32/tests: Print a better error if no Verisign root certificates available.

[Juan Lang]

Hi Austin,

> The error is very cryptic...currently only shows up on OpenSolaris and
> FreeBSD (if /usr/ports/security/ca_root_nss isn't installed). It
> apparently also shows up on some Linux distributions that don't ship
> OpenSSL with any certificates.

While the error may be cryptic, it shows a real bug:  we don't support
the correct root certificate location on OpenSolaris.  As I said
earlier, adding a warning that isn't applicable most of the time
doesn't seem like an appropriate fix.
--Juan