The background context aovids shim blocking when the ctx is cancelled
unexpectedly during shim start. But if the shim exits unexpectedly
before opening the pipe, the fd will never be closed.
`onCloseWithShimLog` makes sure that the shim log fd is closed properly
once the shim disconnects.
Signed-off-by: Li Yuxuan <liyuxuan04@baidu.com>
84464b801f