fix: use aborted property on http request (#1134)

I had some difficulty with this code:

    httpRequest.on('timeout', function () {
      trackFailure('timeout')
      httpRequest.abort()
    })

    httpRequest.on('error', function (err) {
      // Count error if request wasn't aborted due to timeout
      if (!httpRequest.aborted) {
        trackFailure(err)
      }
      callback(err)
    }

When `nock` was not in use, `trackFailure()` would be called once on
timeout.  With `nock` enabled, `trackFailure()` would be called twice
because `httpRequest.aborted` would be undefined.

This change creates and uses the `aborted` property in the same
fashion as the system `http` module.

lib/request_overrider.js

@@ -88,7 +88,6 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
   }
 
   var requestBodyBuffers = [],
-      aborted,
       emitError,
       end,
       ended,
@@ -130,7 +129,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
 
   req.write = function(buffer, encoding, callback) {
     debug('write', arguments);
-    if (!aborted) {
+    if (!req.aborted) {
       if (buffer) {
         if (!Buffer.isBuffer(buffer)) {
           buffer = Buffer.from(buffer, encoding);
@@ -154,7 +153,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
 
   req.end = function(buffer, encoding, callback) {
     debug('req.end');
-    if (!aborted && !ended) {
+    if (!req.aborted && !ended) {
       req.write(buffer, encoding, function () {
         if (typeof callback === 'function') {
           callback();
@@ -164,27 +163,27 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
         req.emit('end');
       });
     }
-    if (aborted) {
+    if (req.aborted) {
       emitError(new Error('Request aborted'));
     }
   };
 
   req.flushHeaders = function() {
     debug('req.flushHeaders');
-    if (!aborted && !ended) {
+    if (!req.aborted && !ended) {
       end(cb);
     }
-    if (aborted) {
+    if (req.aborted) {
       emitError(new Error('Request aborted'));
     }
   };
 
   req.abort = function() {
-    if (aborted) {
+    if (req.aborted) {
       return;
     }
     debug('req.abort');
-    aborted = true;
+    req.aborted = Date.now();
     if (!ended) {
       end();
     }
@@ -456,7 +455,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
       remove(interceptor);
       interceptor.discard();
 
-      if (aborted) { return; }
+      if (req.aborted) { return; }
 
       /// response.client.authorized = true
       /// fixes https://github.com/pgte/nock/issues/158
@@ -493,7 +492,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
 
       function respond() {
 
-        if (aborted) { return; }
+        if (req.aborted) { return; }
 
         if (interceptor.socketDelayInMs && interceptor.socketDelayInMs > 0) {
           req.socket.applyDelay(interceptor.socketDelayInMs);
@@ -507,7 +506,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
         }
 
         function _respond() {
-          if (aborted) { return; }
+          if (req.aborted) { return; }
 
           debug('emitting response');
 
@@ -516,7 +515,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
             cb(response);
           }
 
-          if (aborted) {
+          if (req.aborted) {
             emitError(new Error('Request aborted'));
           }
           else {