* pull: support pulling git-only imports
* pull: also add git imports from external dvc repo
* fetch: add logging
* pull: don't save link to state
When `checkout` or `pull` is done, it'll try to cleanup unused links.
So, when we add from erepo to cache, it creates a link, which DVC will try
to cleanup. Also, it'll provide unwanted checkout change details. So, skipping those
* tests: refactor/rewrite
* flake8: why it's complaining?
* tests: do not leak file descriptors