travis: Run tests against wolfSSL

travis: Run tests against wolfSSL

Check for wolfssl/options.h because if it isn't included, checking other
headers will trigger a warning about hardening the wolfSSL build, which
will cause the check to fail with -Werror.

If the file doesn't exist because user_settings.h is used, the check may
be skipped by configuring with `ac_cv_header_wolfssl_options_h=yes`.