tests: Relax rate limit check for group rate limiter

The rate-limiter worker now is running on Azure VMs whose performance
are more prone to be fluctuate, particularly on block performances. This
commit relaxes the limit check for group rate limiter tests to make them
less flaky.

Signed-off-by: Bo Chen <chen.bo@intel.com>

tests/integration.rs

@@ -10750,7 +10750,7 @@ mod rate_limiter {
             } else {
                 parse_fio_output_iops(&output, &fio_ops, num_queues * num_disks).unwrap()
             };
-            assert!(check_rate_limit(measured_rate, limit_rate, 0.1));
+            assert!(check_rate_limit(measured_rate, limit_rate, 0.2));
         });
 
         let _ = child.kill();