fixes CC-603: move fstype log from generic GetSubvolume to Snapshot/Roll...

...back/Backup/Restore

https://jira.zenoss.com/browse/CC-603

DEMO - starting service:
```
I1216 17:00:44.502433 21417 volume.go:45] Mounting tenantID: 7ltjfw97d0kdi9lege7xsqz0t; baseDir: /home/plu/src/europa/var/serviced/volumes
```

DEMO - snapshot:
```
I1216 17:02:56.184305 21417 snapshot.go:104] Snapshot succeeded for tenantID:7ltjfw97d0kdi9lege7xsqz0t with fsType:rsync using snapshotID:7ltjfw97d0kdi9lege7xsqz0t_20141216-170252
```