lxc: Correctly report active cgroups

There was an inverted return value in lxcCgroupControllerActive().
The function assumes cgroups are active and do couple of checks
to prove that. If any of them fails, false is returned. Therefore,
at the end, after all checks are done we must return true, not false.
(cherry picked from commit 0dddd680)

src/lxc/lxc_driver.c

@@ -1645,7 +1645,7 @@ static bool lxcCgroupControllerActive(virLXCDriverPtr driver,
     if (driver->cgroupControllers & (1 << controller))
         return true;
 #endif
-    return false;
+    return true;
 }