Skip test if too little memory

It required a little more than 500mb of memory which sometimes isn't
available.

server/src/test/java/org/elasticsearch/common/util/BitArrayTests.java

@@ -31,6 +31,8 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
+import static org.hamcrest.Matchers.greaterThanOrEqualTo;
+import static org.junit.Assume.assumeThat;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
@@ -61,8 +63,9 @@ public class BitArrayTests extends ESTestCase {
     }
 
     public void testVeryLarge() {
+        assumeThat(Runtime.getRuntime().maxMemory(), greaterThanOrEqualTo(ByteSizeUnit.MB.toBytes(512)));
         try (BitArray bitArray = new BitArray(1, BigArrays.NON_RECYCLING_INSTANCE)) {
-            long index = randomLongBetween(Integer.MAX_VALUE, ((long) Integer.MAX_VALUE) * 2);
+            long index = randomLongBetween(Integer.MAX_VALUE, (long) (Integer.MAX_VALUE * 1.5));
             assertFalse(bitArray.get(index));
             bitArray.set(index);
             assertTrue(bitArray.get(index));