Fix rsync copying folders

Use --keep-dirlinks to allow rsync copy files to
destination path which is a symlink.

Required because of a commit to devstack:
https://github.com/openstack-dev/devstack/commit/81a016dbcd7bbf9fde791386fcc294fca0a59d71

Change-Id: I47b42adfc70175f5af675573975815066171eac1