Fix crash from property 'browser_version' undefined

When no match is found, the process would just crash. Instead, recognise
this as a normal end-user scenario and point them to the list of
available workers.

In my experience the most common way to encounter this issue is when
additional decimal places are required by the API, e.g. "safari"
"9" results in a crash, because the available workers are described
as "9.1" instead. Given that most browers are described without a
decimal place, this is an easy mistake to make.

Another way to get this is when there is a misspelled browser name.

Before:

```
TypeError: Cannot read property 'browser_version' of undefined
    at browserstack-runner/bin/cli.js
```

After:

```
Error: No desktop match found for {"browser":"safari","browser_version":"9"}
Check https://www.browserstack.com/list-of-browsers-and-platforms/js_testing
    at populateOsAndOsVersion (browserstack-runner/lib/configParser.js)

```

Fixes #243.

Author: Krinkle

lib/configParser.js

@@ -3,6 +3,8 @@
 var Log = require('./logger'),
     logger = new Log(global.logLevel || 'info');
 
+var BROWSER_LIST_URL = 'https://www.browserstack.com/list-of-browsers-and-platforms/js_testing';
+
 var ConfigParser = {
   finalBrowsers: [],
 
@@ -54,10 +56,12 @@ var ConfigParser = {
         var mobileFiltered = ConfigParser.bsBrowsers.filter(function(currentValue) {
           return currentValue.browser.toLowerCase() === browserObject.browser && parseFloat(currentValue.os_version).toPrecision(4) === parseFloat(browserObject.os_version).toPrecision(4);
         });
+        if (!mobileFiltered.length) {
+          throw new Error('No mobile match found for ' + JSON.stringify(browserObject) + '\nCheck ' + BROWSER_LIST_URL);
+        }
 
         browserObject = mobileFiltered[Math.floor(Math.random() * mobileFiltered.length)];
-      }
-      else {
+      } else {
 
         var windowsFiltered = ConfigParser.bsBrowsers.filter(function(currentValue) {
           return currentValue.os === 'Windows' && currentValue.browser_version.match(/metro/i) == null && currentValue.browser === browserObject.browser && ((browserObject.browser_version && browserObject.browser_version.indexOf('latest') > -1) || parseFloat(currentValue.browser_version).toPrecision(4) === parseFloat(browserObject.browser_version).toPrecision(4));
@@ -66,8 +70,13 @@ var ConfigParser = {
         var osxFiltered = ConfigParser.bsBrowsers.filter(function(currentValue) {
           return currentValue.os === 'OS X' && currentValue.browser === browserObject.browser && ((browserObject.browser_version && browserObject.browser_version.indexOf('latest')) > -1 || parseFloat(currentValue.browser_version).toPrecision(4) === parseFloat(browserObject.browser_version).toPrecision(4));
         });
+        // Use Windows VMs if no OS specified
+        var desktopFiltered = windowsFiltered.length > 0 ? windowsFiltered : osxFiltered;
 
-        let filteredObject = windowsFiltered.length > 0 ? windowsFiltered[Math.floor(Math.random() * windowsFiltered.length)] : osxFiltered[Math.floor(Math.random() * osxFiltered.length)];
+        if (!desktopFiltered.length) {
+          throw new Error('No desktop match found for ' + JSON.stringify(browserObject) + '\nCheck ' + BROWSER_LIST_URL);
+        }
+        var filteredObject = desktopFiltered[Math.floor(Math.random() * desktopFiltered.length)];
         if (browserObject.browser_version.indexOf('latest') > -1) {
           filteredObject.browser_version = browserObject.browser_version;
         }
@@ -82,15 +91,14 @@ var ConfigParser = {
     var browserObject = {};
     var version = null;
     var sliceStart = 1;
-    if (typeof(entry) === 'string') {
+    if (typeof entry  === 'string') {
       var browserData = entry.split('_');
       var lindex = browserData.length - 1;
       if (browserData[0] === 'mobile' || browserData[0] === 'android' || (browserData[0] === 'opera' && browserData[1] === 'browser')) {
         browserObject.browser = browserData[0] + ' ' + browserData[1];
         browserObject.mobile = true;
         sliceStart = 2;
-      }
-      else {
+      } else {
         browserObject.browser = browserData[0];
       }
       if (browserData[lindex] && browserData[lindex].indexOf('+') === -1) {
@@ -100,15 +108,13 @@ var ConfigParser = {
         else {
           version = browserData.slice(sliceStart, lindex + 1).join('.');
         }
-      }
-      else {
+      } else {
         version = browserData.slice(sliceStart, lindex + 1).join('.');
       }
       if (browserObject.mobile) {
         browserObject.os_version = version;
         browserObject.browser_version = null;
-      }
-      else {
+      } else {
         browserObject.browser_version = version;
       }
     } else {