Attempt to terminate the process normally (#579)

Fixes microsoft/vscode-java-debug#1274

Author: dsyer

com.microsoft.java.debug.core/src/main/java/com/microsoft/java/debug/core/DebugSession.java

@@ -119,7 +119,9 @@ public void detach() {
 
     @Override
     public void terminate() {
-        if (vm.process() == null || vm.process().isAlive()) {
+        if (vm.process() != null && vm.process().isAlive()) {
+            vm.process().destroy();
+        } else if (vm.process() == null || vm.process().isAlive()) {
             vm.exit(0);
         }
     }