8258512: serviceability/sa/TestJmapCore.java timed out on macOS 10.13.6

Reviewed-by: lmesnik, dcubed

Author: plummercj

test/hotspot/jtreg/serviceability/sa/TestJmapCore.java

@@ -26,7 +26,7 @@
  * @summary Test verifies that jhsdb jmap could generate heap dump from core when heap is full
  * @requires vm.hasSA
  * @library /test/lib
- * @run driver/timeout=240 TestJmapCore run heap
+ * @run driver/timeout=480 TestJmapCore run heap
  */
 
 import java.io.File;