feat(cli): support for multiCapabilities in command line

lib/cli.js

@@ -81,7 +81,7 @@ var flattenObject = function(obj) {
       if (obj.hasOwnProperty(prop)) {
         typeof obj[prop] === 'object' ?
             flattenObject(obj[prop], prefix + prop + '.', out) :
-            out[prefix + prop] = obj[prop];
+            out[prefix + prop] = '' + obj[prop];
       }
     }
   return out;
@@ -91,6 +91,14 @@ if (argv.capabilities) {
   argv.capabilities = flattenObject(argv.capabilities);
 }
 
+if(argv.multiCapabilities) {
+  var multiCapabilitiesArray = [];
+  for (var i = 0; i < Object.keys(argv.multiCapabilities).length; i++) {
+    multiCapabilitiesArray[i] = flattenObject(argv.multiCapabilities[i]);
+  }
+  argv.multiCapabilities = multiCapabilitiesArray;
+}
+
 /**
  * Helper to resolve comma separated lists of file pattern strings relative to
  * the cwd.