libcontainerd/supervisor: store location of pidFile
libcontainerd/supervisor: store location of pidFile

Adding a remote.pidFile to store the location instead of re-constructing its
location each time. Also performing a small refactor to use `strconv.Itoa`
instead of `fmt.Sprintf`.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

Ramzec/docker,moby/moby,Mokolea/docker,konstruktoid/docker-upstream,cpuguy83/docker,moul/docker,trebonian/docker,jimjag/docker,konstruktoid/docker-upstream,jimjag/docker,moby/moby,moul/docker,Mokolea/docker,Ramzec/docker,thaJeztah/docker,trebonian/docker,moul/docker,Mokolea/docker,thaJeztah/docker,Ramzec/docker,cpuguy83/docker,konstruktoid/docker-upstream,moul/docker,Mokolea/docker,trebonian/docker,moby/moby,mahak/docker,cpuguy83/docker,mahak/docker,cpuguy83/docker,Ramzec/docker,konstruktoid/docker-upstream,mahak/docker,trebonian/docker,mahak/docker,thaJeztah/docker,jimjag/docker,moby/moby,jimjag/docker,thaJeztah/docker