In situations where rsync may inadvertently be unable to cleanup it's
temporary files we shouldn't spread them around the cluster.
By asking our rsync subexec to --exclude patterns that match it's own
convention for temporary naming we'll only ever transfer real replicated
artifacts and never temporary artifacts which should always be ignored
until they are fully transfered.
Cleanup of stale rsync droppings should be performed by the auditor and
will be addressed in a separate change related to lp bug #1554005.
Closes-Bug: #1553995
Change-Id: Ibe598b339af024d05e4d89c34d696e972d8189ff
f87a5487b5