Fix failing scaling thread pool test

The previous commit took away the distinction between relying on the
defaults versus relying on an explicit setting for processors. This
commit adds this back, and adjusts the logic to account for the fact
that processors can not exceed available processors any longer.

Author: jasontedor

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

@@ -48,8 +48,17 @@ public void testScalingThreadPoolConfiguration() throws InterruptedException {
             core = "generic".equals(threadPoolName) ? 4 : 1; // the defaults
         }
 
-        final int processors = randomIntBetween(1, Runtime.getRuntime().availableProcessors());
-        final int maxBasedOnNumberOfProcessors = expectedSize(threadPoolName, processors);
+        final int availableProcessors = Runtime.getRuntime().availableProcessors();
+        final int maxBasedOnNumberOfProcessors;
+        final int processors;
+        if (randomBoolean()) {
+            processors = randomIntBetween(1, availableProcessors);
+            maxBasedOnNumberOfProcessors = expectedSize(threadPoolName, processors);
+            builder.put("processors", processors);
+        } else {
+            maxBasedOnNumberOfProcessors = expectedSize(threadPoolName, availableProcessors);
+            processors = availableProcessors;
+        }
 
         final int expectedMax;
         if (maxBasedOnNumberOfProcessors < core || randomBoolean()) {