Fix leak of loop/nbd devices in injection using localfs

Call do_teardown() rather than do_umount()

bug 1130080

Change-Id: I0dd4e4990f75917628007fd380f7df531d9a79e5
Merge "Fix leak of loop/nbd devices in injection using localfs"
Merge remote-tracking branch 'm_src_repo/master' into build-temp