Improve fork harness to allow multiple children and setup pipes automatically.

There was a lot of extra boilerplate involved in setting up pipes so that is now automated.

In some cases testing with multiple children is useful so allow that as well.

test/src/module/common/errorTest.c

@@ -290,12 +290,11 @@ testRun(void)
         // Test in a fork so the process does not actually exit
         HARNESS_FORK_BEGIN()
         {
-            HARNESS_FORK_CHILD()
+            HARNESS_FORK_CHILD_BEGIN(UnhandledError.code, false)
             {
                 THROW(TestChildError, "does not get caught!");
             }
-
-            HARNESS_FORK_CHILD_EXPECTED_EXIT_STATUS_SET(UnhandledError.code);
+            HARNESS_FORK_CHILD_END();
         }
         HARNESS_FORK_END();
     }