Implement snapshot listing in CLI

[ip1981]

USAGE:
    iml snapshot list <fsname> --display <display-type>

For more information try --help
[root@adm ~]# iml snapshot list zfsmo
+------------+----------+---------------------------------+-----------+-------------+
| Filesystem | Snapshot | Creation Time                   | State     | Comment     |
+============+==========+=================================+===========+=============+
| zfsmo      | foo1     | Wed, 09 Sep 2020 12:58:56 +0000 | unmounted | --          |
+------------+----------+---------------------------------+-----------+-------------+
| zfsmo      | foo2     | Wed, 09 Sep 2020 14:01:40 +0000 | unmounted | hello world |
+------------+----------+---------------------------------+-----------+-------------+

Signed-off-by: Igor Pashev pashev.igor@gmail.com

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This change is 

[jgrund]

nit: this should be a fn in iml_manager_client