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/observers/key_observer.rb

@@ -1,9 +1,12 @@
 class KeyObserver < ActiveRecord::Observer
+  include GitHost
+
   def after_save(key)
-    key.update_repository
+    git_host.set_key(key.identifier, key.key, key.projects)
   end
 
   def after_destroy(key)
-    key.repository_delete_key
+    return if key.is_deploy_key && !key.last_deploy?
+    git_host.remove_key(key.identifier, key.projects)
   end
 end