API: fixes visibility of project hook

When a user is not authorized to see the list of hooks for a project, he is
still able to access the hooks separately. For example if access to
`GET /projects/:id/hooks` fails and returns a `403 Unauthorized` error it is
still possible to access a hook directly via `GET /projects/:id/hooks/:hook_id`.

Fixes access, also added tests to check access and status codes of hooks.

lib/api/projects.rb

@@ -155,6 +155,7 @@ module Gitlab
       # Example Request:
       #   GET /projects/:id/hooks/:hook_id
       get ":id/hooks/:hook_id" do
+        authorize! :admin_project, user_project
         @hook = user_project.hooks.find(params[:hook_id])
         present @hook, with: Entities::Hook
       end

spec/requests/api/projects_spec.rb

@@ -196,9 +196,9 @@ describe Gitlab::API do
   end
 
   describe "GET /projects/:id/hooks" do
+    context "authorized user" do
       it "should return project hooks" do
         get api("/projects/#{project.id}/hooks", user)
-
         response.status.should == 200
 
         json_response.should be_an Array
@@ -207,12 +207,34 @@ describe Gitlab::API do
       end
     end
 
+    context "unauthorized user" do
+      it "should not access project hooks" do
+        get api("/projects/#{project.id}/hooks", user3)
+        response.status.should == 403
+      end
+    end
+  end
+
   describe "GET /projects/:id/hooks/:hook_id" do
+    context "authorized user" do
       it "should return a project hook" do
         get api("/projects/#{project.id}/hooks/#{hook.id}", user)
         response.status.should == 200
         json_response['url'].should == hook.url
       end
+
+      it "should return a 404 error if hook id is not available" do
+        get api("/projects/#{project.id}/hooks/1234", user)
+        response.status.should == 404
+      end
+    end
+
+    context "unauthorized user" do
+      it "should not access an existing hook" do
+        get api("/projects/#{project.id}/hooks/#{hook.id}", user3)
+        response.status.should == 403
+      end
+    end
   end
 
   describe "POST /projects/:id/hooks" do