fix: optimize windows-kill execution and silence wmic errors (remy#1720)

This commit silences all errors from the wmic.exe process. Which is save,
because the error case is handled by falling back to the child.pid.

It also optimizes the windows-kill invocation by minimizing (hiding)
the terminal window and keeping it open until the process has finished.

lib/monitor/run.js

@@ -5,6 +5,7 @@ var bus = utils.bus;
 var childProcess = require('child_process');
 var spawn = childProcess.spawn;
 var exec = childProcess.exec;
+var execSync = childProcess.execSync;
 var fork = childProcess.fork;
 var watch = require('./watch').watch;
 var config = require('../config');
@@ -313,25 +314,37 @@ function kill(child, signal, callback) {
   if (utils.isWindows) {
 
     // We are using the Windows Management Instrumentation Command-line
-    // (wmic) to resolve the sub-child process identifier, because the
+    // (wmic.exe) to resolve the sub-child process identifier, because the
     // 'child' process in this context is actually a cmd.exe wrapper.
     // We want to send the termination signal directly to the node process.
-    const resultBuffer = childProcess.execSync(
-      `wmic process where (ParentProcessId=${child.pid}) get ProcessId`
+    // The '2> nul' silences the no process found error message.
+    const resultBuffer = execSync(
+      `wmic process where (ParentProcessId=${child.pid}) get ProcessId 2> nul`
     );
     const result = resultBuffer.toString().match(/^[0-9]+/m);
 
     // If there is no sub-child process we fall back to the child process.
     const processId = Array.isArray(result) ? result[0] : child.pid;
 
+    debug('sending kill signal SIGINT to process: %s', processId);
+
     // We are using the standalone 'windows-kill' executable to send the
-    // standard POSIX signal 'SIGINT' to the process group. This fixes #1720.
+    // standard POSIX signal 'SIGINT' to the node process. This fixes #1720.
+    const windowsKill = path.normalize(
+      `${process.cwd()}/node_modules/nodemon/bin/windows-kill.exe`
+    );
+
+    // We have to detach the 'windows-kill' execution completely from this
+    // process group to avoid terminating the nodemon process itself.
+    // See: https://github.com/alirdn/windows-kill#how-it-works--limitations
     //
-    // We have to detach this binary execution completely via 'start',
-    // because otherwise the nodemon process itself would be terminated:
-    // https://github.com/alirdn/windows-kill#how-it-works--limitations
-    const windowsKill = path.normalize(`${process.cwd()}/node_modules/nodemon/bin/windows-kill.exe`);
-    exec(`start "" ${windowsKill} -SIGINT ${processId}`, callback);
+    // Therefore we are using 'start' to create a new cmd.exe context.
+    // The '/min' option hides the new terminal window and the '/wait'
+    // option lets the process wait for the command to finish.
+    execSync(
+      `start "windows-kill" /min /wait "${windowsKill}" -SIGINT ${processId}`
+    );
+    callback();
 
   } else {
     // we use psTree to kill the full subtree of nodemon, because when