Introduce has_access_to? so that we could reuse it

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7383#note_18439108

app/helpers/projects_helper.rb

@@ -93,10 +93,10 @@ module ProjectsHelper
   end
   def project_for_deploy_key(deploy_key)
-    if deploy_key.projects.include?(@project)
+    if deploy_key.has_access_to?(@project)
       @project
     else
-      deploy_key.projects.find { |project| can?(current_user, :read_project, project) }
+      deploy_key.projects.find(&current_user.method(:has_access_to?))
     end
   end

app/models/deploy_key.rb

@@ -21,7 +21,11 @@ class DeployKey < Key
     self.private?
   end
+  def has_access_to?(project)
+    projects.include?(project)
+  end
+
   def can_push_to?(project)
-    can_push? && projects.include?(project)
+    can_push? && has_access_to?(project)
   end
 end

app/models/user.rb

@@ -501,6 +501,10 @@ class User < ActiveRecord::Base
     several_namespaces? || admin
   end
+  def has_access_to?(project)
+    can?(:read_project, project)
+  end
+
   def can?(action, subject)
     Ability.allowed?(self, action, subject)
   end

lib/gitlab/auth/result.rb

@@ -9,8 +9,7 @@ module Gitlab
       def lfs_deploy_token?(for_project)
         type == :lfs_deploy_token &&
-          actor &&
-          actor.projects.include?(for_project)
+          actor.try(:has_access_to?, for_project)
       end
       def success?

lib/gitlab/git_access.rb

@@ -161,7 +161,7 @@ module Gitlab
     def can_read_project?
       if deploy_key
-        project.public? || deploy_key.projects.include?(project)
+        project.public? || deploy_key.has_access_to?(project)
       elsif user
         user_access.can_read_project?
       else