qemuxml2argvtest: skip test that depends on gnutls_cipher_encrypt()

Test disk-drive-network-rbd-auth-AES depends on existence of
gnutls_cipher_encrypt() function which was introduced in gnutls 2.10.0.
On systems without this function we should skip this test.
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

tests/qemuxml2argvtest.c

@@ -793,8 +793,10 @@ mymain(void)
     DO_TEST("disk-drive-network-rbd", NONE);
     DO_TEST("disk-drive-network-sheepdog", NONE);
     DO_TEST("disk-drive-network-rbd-auth", NONE);
+# ifdef HAVE_GNUTLS_CIPHER_ENCRYPT
     DO_TEST("disk-drive-network-rbd-auth-AES",
             QEMU_CAPS_OBJECT_SECRET);
+# endif
     DO_TEST("disk-drive-network-rbd-ipv6", NONE);
     DO_TEST_FAILURE("disk-drive-network-rbd-no-colon", NONE);
     DO_TEST("disk-drive-no-boot",