Add a simple `api` method to ApiHelpers, replacing api_prefix

See docs for usage

spec/requests/api/issues_spec.rb

 require 'spec_helper'
 
 describe Gitlab::API do
+  include ApiHelpers
+
   let(:user) { Factory :user }
   let!(:project) { Factory :project, owner: user }
   let!(:issue) { Factory :issue, author: user, assignee: user, project: project }

spec/requests/api/projects_spec.rb

 require 'spec_helper'
 
 describe Gitlab::API do
+  include ApiHelpers
+
   let(:user) { Factory :user }
   let!(:project) { Factory :project, owner: user }
   let!(:snippet) { Factory :snippet, author: user, project: project, title: 'example' }

spec/requests/api/users_spec.rb

 require 'spec_helper'
 
 describe Gitlab::API do
+  include ApiHelpers
+
   let(:user) { Factory :user }
 
   describe "GET /users" do

spec/spec_helper.rb

@@ -27,7 +27,6 @@ RSpec.configure do |config|
   config.mock_with :rspec
 
   config.include LoginHelpers, type: :request
-  config.include ApiHelpers,   type: :request
 
   # If you're not using ActiveRecord, or you'd prefer not to run each of your
   # examples within a transaction, remove the following line or assign false

spec/support/api_helpers.rb

 module ApiHelpers
-  def api_prefix
-    "/api/#{Gitlab::API::VERSION}"
+  # Public: Prepend a request path with the path to the API
+  #
+  # path - Path to append
+  # user - User object - If provided, automatically appends private_token query
+  #          string for authenticated requests
+  #
+  # Examples
+  #
+  #   >> api('/issues')
+  #   => "/api/v2/issues"
+  #
+  #   >> api('/issues', User.last)
+  #   => "/api/v2/issues?private_token=..."
+  #
+  #   >> api('/issues?foo=bar', User.last)
+  #   => "/api/v2/issues?foo=bar&private_token=..."
+  #
+  # Returns the relative path to the requested API resource
+  def api(path, user = nil)
+    "/api/#{Gitlab::API::VERSION}#{path}" +
+
+      # Normalize query string
+      (path.index('?') ? '' : '?') +
+
+      # Append private_token if given a User object
+      (user.respond_to?(:private_token) ?
+        "&private_token=#{user.private_token}" : "")
   end
 
   def json_response