Fix scaling thread pool test bug

This commit fixes a test bug in the scaling thread pool configuration
test. In particular, the test randomization could select min and max for
a thread pool configuration where both are equal to zero. This is a
violation of the requirements of the ThreadPoolExecutor. With this
commit, we now ensure that the max is bounded below by one.

core/src/test/java/org/elasticsearch/threadpool/ScalingThreadPoolTests.java

@@ -59,7 +59,7 @@ public class ScalingThreadPoolTests extends ESThreadPoolTestCase {
 
         final int expectedSize;
         if (sizeBasedOnNumberOfProcessors < min || randomBoolean()) {
-            expectedSize = randomIntBetween(min, 16);
+            expectedSize = randomIntBetween(Math.max(1, min), 16);
             builder.put("threadpool." + threadPoolName + ".size", expectedSize);
         }  else {
             expectedSize = sizeBasedOnNumberOfProcessors;