This commit containers the following changes:
- Fix fd forwarding in exec
- Fix exists_exec algorithm for path to executable contains symlinks parent
- Fix mount destination when using as alias
- Add Device directive for changing devfs rules
Previously the checks and global resource allocation all happen in one place, this commit
move out the checks that does not require resource allocation. This allows us to warn the
user ahead of time about potentially risky container creation without restore allocated
resources.