tests: Don't build securityselinuxlabeltest without qemu

Sources for securityselinuxlabeltest are only defined if qemu driver is
enabled so we should not try to build the test if qemu driver is
disabled.
(cherry picked from commit d6c85970)

tests/Makefile.am

@@ -108,10 +108,12 @@ endif
 
 if WITH_SECDRIVER_SELINUX
 test_programs += securityselinuxtest
+if WITH_QEMU
 if WITH_ATTR
 test_programs += securityselinuxlabeltest
 endif
 endif
+endif
 
 if WITH_DRIVER_MODULES
 test_programs += virdrivermoduletest