We sometimes see probe test failures in the gate where `resetswift`
fails like
umount: /mnt/sdb1: target is busy.
It seems to be because `swift-init all kill` is just a stop with a
status check after the fact. Add an orphan sweep afterwards to make
sure worker subprocesses got cleaned up, too.
Change-Id: I533b436a35e5c3deb7488e9961b55f2274c14751
6c360a70bf