MaybeRegister() calls Register() if the current context is a rootless one, or if the "container" environment variable suggests that we're in a container.

Register() registers binfmt.d emulators described by configuration files in the passed-in slice of directories, or in the union of /etc/binfmt.d, /run/binfmt.d, and /usr/lib/binfmt.d if the slice has no items.