Fix `U2fSpec` for PhantomJS versions > 2.

- We weren't explicilty waiting for the page to load while navigating
  to the "Manage two-factor authentication" page. This was probably
  incidentally working for PhantomJS 1.x versions.

spec/features/u2f_spec.rb

 require 'spec_helper'
 
 feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature: true, js: true do
+  include WaitForAjax
+
   before { allow_any_instance_of(U2fHelper).to receive(:inject_u2f_api?).and_return(true) }
 
+  def manage_two_factor_authentication
+    click_on 'Manage Two-Factor Authentication'
+    expect(page).to have_content("Setup New U2F Device")
+    wait_for_ajax
+  end
+
   def register_u2f_device(u2f_device = nil)
     u2f_device ||= FakeU2fDevice.new(page)
     u2f_device.respond_to_u2f_registration
@@ -34,7 +42,7 @@ feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature:
     describe 'when 2FA via OTP is enabled' do
       it 'allows registering a new device' do
         visit profile_account_path
-        click_on 'Manage Two-Factor Authentication'
+        manage_two_factor_authentication
         expect(page.body).to match("You've already enabled two-factor authentication using mobile")
 
         register_u2f_device
@@ -46,15 +54,15 @@ feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature:
         visit profile_account_path
 
         # First device
-        click_on 'Manage Two-Factor Authentication'
+        manage_two_factor_authentication
         register_u2f_device
         expect(page.body).to match('Your U2F device was registered')
 
         # Second device
-        click_on 'Manage Two-Factor Authentication'
+        manage_two_factor_authentication
         register_u2f_device
         expect(page.body).to match('Your U2F device was registered')
-        click_on 'Manage Two-Factor Authentication'
+        manage_two_factor_authentication
         expect(page.body).to match('You have 2 U2F devices registered')
       end
     end
@@ -62,7 +70,7 @@ feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature:
     it 'allows the same device to be registered for multiple users' do
       # First user
       visit profile_account_path
-      click_on 'Manage Two-Factor Authentication'
+      manage_two_factor_authentication
       u2f_device = register_u2f_device
       expect(page.body).to match('Your U2F device was registered')
       logout
@@ -71,7 +79,7 @@ feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature:
       user = login_as(:user)
       user.update_attribute(:otp_required_for_login, true)
       visit profile_account_path
-      click_on 'Manage Two-Factor Authentication'
+      manage_two_factor_authentication
       register_u2f_device(u2f_device)
       expect(page.body).to match('Your U2F device was registered')
 
@@ -81,7 +89,7 @@ feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature:
     context "when there are form errors" do
       it "doesn't register the device if there are errors" do
         visit profile_account_path
-        click_on 'Manage Two-Factor Authentication'
+        manage_two_factor_authentication
 
         # Have the "u2f device" respond with bad data
         page.execute_script("u2f.register = function(_,_,_,callback) { callback('bad response'); };")
@@ -96,7 +104,7 @@ feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature:
 
       it "allows retrying registration" do
         visit profile_account_path
-        click_on 'Manage Two-Factor Authentication'
+        manage_two_factor_authentication
 
         # Failed registration
         page.execute_script("u2f.register = function(_,_,_,callback) { callback('bad response'); };")
@@ -122,7 +130,7 @@ feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature:
       login_as(user)
       user.update_attribute(:otp_required_for_login, true)
       visit profile_account_path
-      click_on 'Manage Two-Factor Authentication'
+      manage_two_factor_authentication
       @u2f_device = register_u2f_device
       logout
     end
@@ -161,7 +169,7 @@ feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature:
           current_user = login_as(:user)
           current_user.update_attribute(:otp_required_for_login, true)
           visit profile_account_path
-          click_on 'Manage Two-Factor Authentication'
+          manage_two_factor_authentication
           register_u2f_device
           logout
 
@@ -182,7 +190,7 @@ feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature:
           current_user = login_as(:user)
           current_user.update_attribute(:otp_required_for_login, true)
           visit profile_account_path
-          click_on 'Manage Two-Factor Authentication'
+          manage_two_factor_authentication
           register_u2f_device(@u2f_device)
           logout
 
@@ -248,7 +256,7 @@ feature 'Using U2F (Universal 2nd Factor) Devices for Authentication', feature:
         user = login_as(:user)
         user.update_attribute(:otp_required_for_login, true)
         visit profile_account_path
-        click_on 'Manage Two-Factor Authentication'
+        manage_two_factor_authentication
         expect(page).to have_content("Your U2F device needs to be set up.")
         register_u2f_device
       end