Use similar interface to access gitolite

Simplified gitolite handle logic
Stubn over monkeypatch
Stub only specific methods in Gitlab:Gitolite
Moved grach auth to lib
added specs for keys observer
removes SshKey role

app/models/protected_branch.rb

@@ -1,4 +1,6 @@
 class ProtectedBranch < ActiveRecord::Base
+  include GitHost
+
   belongs_to :project
   validates_presence_of :project_id
   validates_presence_of :name
@@ -7,7 +9,7 @@ class ProtectedBranch < ActiveRecord::Base
   after_destroy :update_repository
 
   def update_repository
-    Gitlab::GitHost.system.update_project(project.path, project)
+    git_host.update_repository(project)
   end
 
   def commit