test: forbid common.mustCall*() in process exit handlers

`common.mustCall()` and `common.mustCallAtLeast()` need to be called
before process exit handlers to work because checks are done inside a
process exit handler. Detect if being used inside a process exit handler
and throw.

PR-URL: https://github.com/nodejs/node/pull/17453
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/common/index.js

@@ -493,6 +493,8 @@ exports.mustCallAtLeast = function(fn, minimum) {
 };
 
 function _mustCallInner(fn, criteria = 1, field) {
+  if (process._exiting)
+    throw new Error('Cannot use common.mustCall*() in process exit handler');
   if (typeof fn === 'number') {
     criteria = fn;
     fn = noop;