Reduce stressTestMultiplier to 25 (from 30) in stress test mode;

Introduce stressTestMultiplierSqrt that is a square root of stressTestMultiplier

Author: elizarov

core/kotlinx-coroutines-core/src/test/kotlin/kotlinx/coroutines/experimental/TestBase.kt

@@ -47,10 +47,12 @@ public actual open class TestBase actual constructor() {
      */
     public actual val isStressTest = System.getProperty("stressTest") != null
 
+    public val stressTestMultiplierSqrt = if (isStressTest) 5 else 1
+
     /**
      * Multiply various constants in stress tests by this factor, so that they run longer during nightly stress test.
      */
-    public actual val stressTestMultiplier = if (isStressTest) 30 else 1
+    public actual val stressTestMultiplier = stressTestMultiplierSqrt * stressTestMultiplierSqrt
 
     private var actionIndex = AtomicInteger()
     private var finished = AtomicBoolean()