Idempotency for LXC cloning

Previously, clone operations where the new container already exists were reporting as failed. This commit modifies that behavior so that if the new container exists, it returns the facts for that container instead of failing.

To do this, changes were made to the logic of `_get_container_info` to return an empty dict when the container does not exist rather than issuing a hard fail.

I also made a few fixes in the documentation by removing trailing spaces and fixing a typo in the state on line 222.