The ShimManager.Start() will call loadShim() to get the existing shim if SandboxID
is specified for a container, but shimTask.PID() is called in loadShim,
which will call Connect() of Task API with the ID of a task that is not
created yet(containerd is getting the shim and Task API address to call
Create, so the task is not created yet).
In this commit we change the logic of loadShim() to get the shim without calling
Connect() of the not created container ID.
Signed-off-by: Abel Feng <fshb1988@gmail.com>