optimize sandbox directory structure

[Vanient]

1. As we just need to mount guest needed directory and files to guest, other files like console sock and sandbox.json should not be mounted into guest, so we create a shared directory to store those needed by guest and mount it only.

after optimizing:

2. create bundle directory earlier Before this, container bundle directory was initialized and created in spec handler, but it was used by storage handler and io handler which before spec handler, bundle directory was still "" in storage handler and io handler, which caused files were created under "/". So we should initialize and create bundle directory in metadata add handler which is before all other ones.

[abel-von]

LGTM