qemuhotplugtest: Don't leak @vm

Some tests take already prepared domain from previous tests. In
this case, the domain is freed by the first test that doesn't
keep the domain. However, if there's no such test case domain is
leaked.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

tests/qemuhotplugtest.c

@@ -855,6 +855,7 @@ mymain(void)
     DO_TEST_CPU_INDIVIDUAL("ppc64-modern-individual", "17", true, true, true);
 
     qemuTestDriverFree(&driver);
+    virObjectUnref(data.vm);
     return (ret == 0) ? EXIT_SUCCESS : EXIT_FAILURE;
 }