Use os.path.join() instead of string concatenation in actions
Use os.path.join() instead of string concatenation in actions

Presence of / in action is not a problem at is check for early. Any other tricks
are secured against by the realpath() check immediately afterwards.
freedomboxtwh/Plinth,vignanl/Plinth,vignanl/Plinth,kkampardi/Plinth,kkampardi/Plinth,kkampardi/Plinth,harry-7/Plinth,kkampardi/Plinth,freedomboxtwh/Plinth,jvalleroy/plinth-debian,freedomboxtwh/Plinth,kkampardi/Plinth,vignanl/Plinth,harry-7/Plinth,freedomboxtwh/Plinth,jvalleroy/plinth-debian,jvalleroy/plinth-debian,jvalleroy/plinth-debian,harry-7/Plinth,harry-7/Plinth,jvalleroy/plinth-debian,vignanl/Plinth,vignanl/Plinth,freedomboxtwh/Plinth,harry-7/Plinth