crypto: use error_abort for unexpected failures

This improves the error diagnosis from the unit test when a cipher
is unexpected not available from

ERROR:../tests/unit/test-crypto-cipher.c:683:test_cipher: assertion failed: (err == NULL)
Bail out! ERROR:../tests/unit/test-crypto-cipher.c:683:test_cipher: assertion failed: (err == NULL)
Aborted (core dumped)

to

Unexpected error in qcrypto_cipher_ctx_new() at ../crypto/cipher-gcrypt.c.inc:262:
./build//tests/unit/test-crypto-cipher: Cannot initialize cipher: Invalid cipher algorithm
Aborted (core dumped)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

tests/unit/test-crypto-cipher.c

@@ -676,9 +676,8 @@ static void test_cipher(const void *opaque)
     cipher = qcrypto_cipher_new(
         data->alg, data->mode,
         key, nkey,
-        &err);
+        data->plaintext ? &error_abort : &err);
     if (data->plaintext) {
-        g_assert(err == NULL);
         g_assert(cipher != NULL);
     } else {
         error_free_or_abort(&err);