boot-serial-test: prefer tcg accelerator

Prefer to use the tcg accelarator if it is available: This is our only
real smoke test for tcg, and fast enough to use it for that.

Fixes: 480bc11e6 ("boot-serial-test: fallback to kvm accelerator")
Reported-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/boot-serial-test.c

@@ -78,7 +78,11 @@ static void test_machine(const void *data)
     fd = mkstemp(tmpname);
     g_assert(fd != -1);
 
-    args = g_strdup_printf("-M %s,accel=kvm:tcg "
+    /*
+     * Make sure that this test uses tcg if available: It is used as a
+     * fast-enough smoketest for that.
+     */
+    args = g_strdup_printf("-M %s,accel=tcg:kvm "
                            "-chardev file,id=serial0,path=%s "
                            "-no-shutdown -serial chardev:serial0 %s",
                            test->machine, tmpname, test->extra);