this adds a `platform` interface for shim service to manage platform-specific
behaviors such as I/O (which uses epoll in linux to work around bugs with applications
that closes all consoles i.e. https://github.com/opencontainers/runc/pull/1434
and https://github.com/moby/moby/issues/27202)
Its expected that we only have 1 epollfd per containerd_shim to manage all processes.
Since all the work are done outside of the container runtime, upgrading of runc
is not required and should be done separately.
Signed-off-by: Daniel Dao <dqminh89@gmail.com>
