Fix validation of hostPath

When adding a volume, this comes in mountOptions. The hostPath in the
database is the computed host path.

dashboard/src/js/client.js

@@ -3320,13 +3320,12 @@ angular.module('Application').service('Client', ['$http', '$interval', '$timeout
         });
     };
 
-    Client.prototype.addVolume = function (name, mountType, hostPath, mountOptions, callback) {
+    Client.prototype.addVolume = function (name, mountType, mountOptions, callback) {
         var data = {
             name: name,
             mountType: mountType,
             mountOptions: mountOptions
         };
-        if (hostPath) data.hostPath = hostPath;
 
         post('/api/v1/volumes', data, null, function (error, data, status) {
             if (error) return callback(error);