Ensure swift.conf created in all scenarios

Change I60fb78e5d40605ab47f349d154737ef9bab641f4 introduced a bug
wherein /etc/swift/swift.conf is getting created in consolidated
installs in which openstack::swift::proxy and
openstack::swift::storage-node classes are both applied to the same
server, but is not getting created on storage nodes in distributed
installs in which the proxy and storage-node classes are applied to
different servers.

Use ensure_resource wrappers around the swift class call to correct.

Change-Id: I692ddf5f344577705fc6a8652349f480ad21542d
Closes-Bug: 1287349
(cherry picked from commit 472253cbe29b1375b33d91ae13b561dcdc7fa2d6)
Merge remote-tracking branch 'origin/stable/havana' into havana