perf: checkout: subsequent runs slow

[casperdcl]

Running dvc checkout multiple times shows slow progress going through all files rather than returning quickly. Using local remote (both on a different drive as well as same drive):

DVC version: 0.83.0
Python version: 3.6.9
Platform: Linux-4.15.0-58-generic-x86_64-with-Ubuntu-16.04-xenial
Binary: False
Package: snap
Cache: reflink - not supported, hardlink - supported, symlink - supported

[dberenbaum]

@dtrifiro dvc checkout performance on subsequent runs could be a good area to research. Let's consider what the priority should be for this.

[efiop]

There have been a lot of improvements in checkout department. Closing as stale.