Current Swift playbook is based on the preassumption of AIO setup.
However, if one goes with default multinode setup
(ansible/inventory/multinode), it follows the P + ACO deployment model,
which proxy-server runs on controller nodes where ACO
(account/container/object services) run on storage nodes.

It will break because swift proxy-server no longer has access (it
shouldn't have) to /srv/node path. This change ensure disk mounting part
only happens on storage node. It also moves chown from proxy-server
Dockerfile to rsyncd because no matter with PACO, P+ACO or P+A+C+O
model, rsyncd is always running on each storage node.

Change-Id: I3aa20454902caa9c84d3901bb91e4e4c93ac5f34
Partially-Implements: blueprint swift-physical-disk
Closes-Bug: #1537544