cmd/zfs: support creating parents with canmount=no
#975
| Job | Run time |
|---|---|
| 11s | |
| 4h 7m 7s | |
| 3h 29m 8s | |
| 3h 56m 59s | |
| 4h 45m 4s | |
| 3h 27m 41s | |
| 3h 23m 25s | |
| 2h 23m 29s | |
| 2h 20m 0s | |
| 2h 27m 34s | |
| 2m 44s | |
| 4h 39m 11s | |
| 3h 33m 35s | |
| 4h 15m 58s | |
| 3h 46m 28s | |
| 33s | |
| 1d 22h 39m 7s |