some fatal -> fatalx to improved logging

some fatal -> fatalx to improved logging

errno doesn't generally contains anything useful after libtls functions,
and in most cases it's explicitly cleared to avoid misuse, so change a
few fatal() calls to fatalx() when logging libtls failures.  Also, add
the real error string, via tls_error() or tls_config_error(), that was
missing before.

ok millert@