test: move some test from sequential to parallel

The only test with modifications is `test-stdin-child-proc` that was
passing when it should not because the exit code of the child process
was not being checked.

PR-URL: #6087
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Claudio Rodriguez <cjrodr@yahoo.com>

test/parallel/test-stdin-child-proc.js

@@ -0,0 +1,13 @@
+'use strict';
+// This tests that pausing and resuming stdin does not hang and timeout
+// when done in a child process.  See test/parallel/test-stdin-pause-resume.js
+const common = require('../common');
+const assert = require('assert');
+const child_process = require('child_process');
+const path = require('path');
+const cp = child_process.spawn(process.execPath,
+                    [path.resolve(__dirname, 'test-stdin-pause-resume.js')]);
+
+cp.on('exit', common.mustCall((code) => {
+  assert.equal(code, 0);
+}));